SUMMARY
Trying to dock a docker created by pykrita (either floating, or already docked somewhere else) causes a SIGSEGV. Originally I found this problem with a third-party plugin, but then I reproduced it with the built-in comic manager and last documents pykrita plugins, so I think this is a problem with pykrita and not the actual python scripts. Also, I can dock built-in dockers without problem, only dockers created by python scripts crash.

>>> bt full
#0  0x0000000000000000 in  ()
#1  0x00007ffff5a94319 in QMetaObject::cast(QObject const*) const (this=0x7ffff6c97b40 <QWidgetWindow::staticMetaObject>, obj=0x555559f45e50) at /usr/src/debug/dev-qt/qtcore-5.15.7/qtbase-everywhere-src-5.15.7/src/corelib/kernel/qmetaobject.cpp:389
#2  0x00007ffff5a94355 in QMetaObject::cast(QObject*) const (this=<optimized out>, obj=<optimized out>) at /usr/src/debug/dev-qt/qtcore-5.15.7/qtbase-everywhere-src-5.15.7/src/corelib/kernel/qmetaobject.cpp:378
#3  0x00007ffff679b53b in qobject_cast<QWidgetWindow*>(QObject*) (object=<optimized out>) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/include/QtCore/../../src/corelib/kernel/qobject.h:519
        q = 0x555559f45950
        window = <optimized out>
#4  QWidgetPrivate::show_sys() (this=this@entry=0x555559f459d0) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qwidget.cpp:7869
        q = 0x555559f45950
        window = <optimized out>
#5  0x00007ffff67a482b in QWidgetPrivate::show_helper() (this=0x555559f459d0) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qwidget.cpp:7839
        q = 0x555559f45950
        isWindow = <optimized out>
        isEmbedded = false
        showEvent = {
          <QEvent> = {
            _vptr.QEvent = 0x7ffff64538e0 <vtable for QShowEvent+16>,
            static staticMetaObject = {
              d = {
                superdata = {
                  direct = 0x0
                },
                stringdata = 0x7ffff5c3f320 <qt_meta_stringdata_QEvent>,
                data = 0x7ffff5c3ed60 <qt_meta_data_QEvent>,
                static_metacall = 0x0,
                relatedMetaObjects = 0x0,
                extradata = 0x0
              }
            },
            d = 0x0,
            t = 17,
            posted = 0,
            spont = 0,
            m_accept = 1,
            reserved = 2878
          }, <No data fields>}
#6  0x00007ffff67a45fb in QWidgetPrivate::show_recursive() (this=<optimized out>) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qwidget.cpp:7716
#7  0x00007ffff67a4789 in QWidgetPrivate::showChildren(bool) (this=this@entry=0x555559f3ecc0, spontaneous=spontaneous@entry=false) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qwidget.h:132
        widget = <optimized out>
        i = 2
        childList = {
          <QListSpecialMethods<QObject*>> = {<No data fields>},
          members of QList<QObject*>:
          {
            p = {
              static shared_null = {
                ref = {
                  atomic = {
                    _q_value = std::atomic<int> = { -1 }
                  }
                },
                alloc = 0,
                begin = 0,
                end = 0,
                array = {[0] = 0x0}
              },
              d = 0x555559f48200
            },
            d = 0x555559f48200
          }
        }
#8  0x00007ffff67a47ff in QWidgetPrivate::show_helper() (this=0x555559f3ecc0) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qwidget.cpp:7792
        q = 0x555559f3bff0
        isWindow = <optimized out>
        isEmbedded = <optimized out>
        showEvent = {
          <QEvent> = {
            _vptr.QEvent = 0x555559f3b080,
            static staticMetaObject = {
              d = {
                superdata = {
                  direct = 0x0
                },
                stringdata = 0x7ffff5c3f320 <qt_meta_stringdata_QEvent>,
                data = 0x7ffff5c3ed60 <qt_meta_data_QEvent>,
                static_metacall = 0x0,
                relatedMetaObjects = 0x0,
                extradata = 0x0
              }
            },
            d = 0x7ffff679a7a7 <QWidget::setAttribute(Qt::WidgetAttribute, bool)+295>,
            t = 0,
            posted = 0,
            spont = 0,
            m_accept = 0,
            reserved = 0
          }, <No data fields>}
#9  0x00007ffff67a45fb in QWidgetPrivate::show_recursive() (this=<optimized out>) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qwidget.cpp:7716
#10 0x00007ffff67a4789 in QWidgetPrivate::showChildren(bool) (this=this@entry=0x555559f398b0, spontaneous=spontaneous@entry=false) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qwidget.h:132
        widget = <optimized out>
        i = 4
        childList = {
          <QListSpecialMethods<QObject*>> = {<No data fields>},
          members of QList<QObject*>:
          {
            p = {
              static shared_null = {
                ref = {
                  atomic = {
                    _q_value = std::atomic<int> = { -1 }
                  }
                },
                alloc = 0,
                begin = 0,
                end = 0,
                array = {[0] = 0x0}
              },
              d = 0x555559f4eb00
            },
            d = 0x555559f4eb00
          }
        }
#11 0x00007ffff67a47ff in QWidgetPrivate::show_helper() (this=this@entry=0x555559f398b0) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qwidget.cpp:7792
        q = 0x555559f3b080
        isWindow = <optimized out>
        isEmbedded = <optimized out>
        showEvent = {
          <QEvent> = {
            _vptr.QEvent = 0x555557c0f870,
            static staticMetaObject = {
              d = {
                superdata = {
                  direct = 0x0
                },
                stringdata = 0x7ffff5c3f320 <qt_meta_stringdata_QEvent>,
                data = 0x7ffff5c3ed60 <qt_meta_data_QEvent>,
                static_metacall = 0x0,
                relatedMetaObjects = 0x0,
                extradata = 0x0
              }
            },
            d = 0x0,
            t = 49264,
            posted = 1,
            spont = 0,
            m_accept = 1,
            reserved = 2809
          }, <No data fields>}
#12 0x00007ffff67a77d3 in QWidgetPrivate::setVisible(bool) (this=0x555559f398b0, visible=<optimized out>) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qwidget.cpp:8135
        pw = <optimized out>
        wasResized = true
        initialWindowState = {
          i = 0
        }
        needUpdateGeometry = <optimized out>
        showToParentEvent = {
          _vptr.QEvent = 0x1,
          static staticMetaObject = {
            d = {
              superdata = {
                direct = 0x0
              },
              stringdata = 0x7ffff5c3f320 <qt_meta_stringdata_QEvent>,
              data = 0x7ffff5c3ed60 <qt_meta_data_QEvent>,
              static_metacall = 0x0,
              relatedMetaObjects = 0x0,
              extradata = 0x0
            }
          },
          d = 0x0,
          t = 2904,
          posted = 1,
          spont = 0,
          m_accept = 1,
          reserved = 2809
        }
        q = 0x555559f3b080
#13 0x00007ffff67a7ab2 in QWidget::setVisible(bool) (this=this@entry=0x555559f3b080, visible=visible@entry=true) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qwidget.cpp:8067
        d = <optimized out>
#14 0x00007fffbb14878b in sipDockWidget::setVisible(bool) (this=0x555559f3b080, a0=<optimized out>) at /usr/src/debug/media-gfx/krita-5.1.4-r1/krita-5.1.4_build/plugins/extensions/pykrita/sip/_tmp/krita/sipkritapart0.cpp:25244
        sipGILState = (PyGILState_UNLOCKED | unknown: 0x5554)
        sipMeth = <optimized out>
#15 0x00007ffff688d9b8 in QDockWidgetPrivate::setWindowState(bool, bool, QRect const&) (this=0x555559f398b0, floating=floating@entry=false, unplug=unplug@entry=false, rect=...) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/widgets/qdockwidget.cpp:1179
        q = 0x555559f3b080
        wasFloating = <optimized out>
        hidden = false
        flags = {
          i = <optimized out>
        }
        dwLayout = <optimized out>
        nativeDeco = false
#16 0x00007ffff688da3c in QDockWidgetPrivate::plug(QRect const&) (this=<optimized out>, rect=...) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/widgets/qdockwidget.cpp:1132
#17 0x00007ffff68d11b6 in QMainWindowLayout::animationFinished(QWidget*) (this=0x555557cd0590, widget=<optimized out>) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/widgets/qmainwindowlayout.cpp:2244
        dw = 0x555559f3b080
#18 0x00007ffff685bc59 in QWidgetAnimator::animate(QWidget*, QRect const&, bool) (this=this@entry=0x555557cd0b30, widget=<optimized out>, widget@entry=0x555559f3b080, _final_geometry=..., animate=false) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/widgets/qwidgetanimator.cpp:120
        animationDuration = 0
        final_geometry = {
          x1 = 1627,
          y1 = 641,
          x2 = 1920,
          y2 = 978
        }
#19 0x00007ffff68cdcbc in QMainWindowLayout::plug(QLayoutItem*) (this=this@entry=0x555557cd0590, widgetItem=<optimized out>) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/widgets/qmainwindowlayout.cpp:2167
        widget = 0x555559f3b080
        groups = {
          <QListSpecialMethods<QDockWidgetGroupWindow*>> = {<No data fields>},
          members of QList<QDockWidgetGroupWindow*>:
          {
            p = {
              static shared_null = {
                ref = {
                  atomic = {
                    _q_value = std::atomic<int> = { -1 }
                  }
                },
                alloc = 0,
                begin = 0,
                end = 0,
                array = {[0] = 0x0}
              },
              d = 0x7ffff5b605f0 <QListData::shared_null>
            },
            d = 0x7ffff5b605f0 <QListData::shared_null>
          }
        }
        previousPath = {
          <QListSpecialMethods<int>> = {<No data fields>},
          members of QList<int>:
          {
            p = {
              static shared_null = {
                ref = {
                  atomic = {
                    _q_value = std::atomic<int> = { -1 }
                  }
                },
                alloc = 0,
                begin = 0,
                end = 0,
                array = {[0] = 0x0}
              },
              d = 0x7fffcc007750
            },
            d = 0x7fffcc007750
          }
        }
        it = <optimized out>
        globalRect = {
          x1 = 1627,
          y1 = 641,
          x2 = 1920,
          y2 = 978
        }
#20 0x00007ffff688c8ea in QDockWidgetPrivate::endDrag(bool) (this=this@entry=0x555559f398b0, abort=abort@entry=false) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/widgets/qdockwidget.cpp:848
        mainWindow = 0x555557c0f870
        mwLayout = 0x555557cd0590
        q = 0x555559f3b080
#21 0x00007ffff68903f1 in QDockWidgetPrivate::mouseReleaseEvent(QMouseEvent*) (event=0x7fffffffc700, this=<optimized out>) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/widgets/qdockwidget.cpp:1022
        d = <optimized out>
        win = 0x555557c0f870
        layout = <optimized out>
#22 QDockWidgetPrivate::mouseReleaseEvent(QMouseEvent*) (event=0x7fffffffc700, this=<optimized out>) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/widgets/qdockwidget.cpp:1017
        d = <optimized out>
        win = 0x555557c0f870
        layout = <optimized out>
#23 QDockWidget::event(QEvent*) (this=this@entry=0x555559f3b080, event=event@entry=0x7fffffffc700) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/widgets/qdockwidget.cpp:1597
        d = <optimized out>
        win = 0x555557c0f870
        layout = <optimized out>
#24 0x00007fffbb153ecb in sipDockWidget::event(QEvent*) (this=0x555559f3b080, a0=0x7fffffffc700) at /usr/src/debug/media-gfx/krita-5.1.4-r1/krita-5.1.4_build/plugins/extensions/pykrita/sip/_tmp/krita/sipkritapart0.cpp:25306
        sipGILState = (PyGILState_UNLOCKED | unknown: 0x5554)
        sipMeth = <optimized out>
#25 0x00007ffff67633fe in QApplicationPrivate::notify_helper(QObject*, QEvent*) (this=this@entry=0x555555e81150, receiver=receiver@entry=0x555559f3b080, e=e@entry=0x7fffffffc700) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qapplication.cpp:3637
        consumed = false
        filtered = false
#26 0x00007ffff676bea0 in QApplication::notify(QObject*, QEvent*) (this=this@entry=0x7fffffffcff0, receiver=receiver@entry=0x555559f3b080, e=e@entry=0x7fffffffc700) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qapplication.cpp:3081
        me = {
          <QInputEvent> = {
            <QEvent> = {
              _vptr.QEvent = 0x7ffff64535a0 <vtable for QMouseEvent+16>,
              static staticMetaObject = {
                d = {
                  superdata = {
                    direct = 0x0
                  },
                  stringdata = 0x7ffff5c3f320 <qt_meta_stringdata_QEvent>,
                  data = 0x7ffff5c3ed60 <qt_meta_data_QEvent>,
                  static_metacall = 0x0,
                  relatedMetaObjects = 0x0,
                  extradata = 0x0
                }
              },
              d = 0x0,
              t = 3,
              posted = 0,
              spont = 1,
              m_accept = 1,
              reserved = 0
            },
            members of QInputEvent:
            modState = {
              i = 0
            },
            ts = 73748715
          },
          members of QMouseEvent:
          l = {
            xp = 41,
            yp = 7
          },
          w = {
            xp = 41,
            yp = 7
          },
          s = {
            xp = 1734,
            yp = 886
          },
          b = Qt::LeftButton,
          mouseState = {
            i = 0
          },
          caps = 0,
          velocity = {
            v = {[0] = 0, [1] = 0}
          }
        }
        w = 0x555559f3b080
        mouse = 0x7fffffffc700
        eventAccepted = <optimized out>
        relpos = {
          xp = 41,
          yp = 7
        }
        d = 0x555555e81150
        res = false
#27 0x00007ffff7aeb79e in KisApplication::notify(QObject*, QEvent*) (this=0x7fffffffcff0, receiver=0x555559f3b080, event=0x7fffffffc700) at /usr/src/debug/media-gfx/krita-5.1.4-r1/krita-5.1.4/libs/ui/KisApplication.cpp:762
        guard = {
          m_info = 0x5555565759a0
        }
        result = true
        info = @0x5555565759a0: {
          eventRecursionCount = 2,
          postponedSynchronizationEvents = std::queue wrapping: std::deque with 0 elements
        }
#28 0x00007ffff5a8b548 in QCoreApplication::notifyInternal2(QObject*, QEvent*) (receiver=0x555559f3b080, event=0x7fffffffc700) at /usr/src/debug/dev-qt/qtcore-5.15.7/qtbase-everywhere-src-5.15.7/src/corelib/kernel/qcoreapplication.cpp:1064
        selfRequired = true
        result = false
        cbdata = {[0] = 0x555559f3b080, [1] = 0x7fffffffc700, [2] = 0x7fffffffc4ef}
        d = <optimized out>
        threadData = 0x555555e6cc80
        scopeLevelCounter = {
          threadData = 0x555555e6cc80
        }
#29 0x00007ffff6769ef4 in QApplicationPrivate::sendMouseEvent(QWidget*, QMouseEvent*, QWidget*, QWidget*, QWidget**, QPointer<QWidget>&, bool, bool) (receiver=receiver@entry=0x555559f3b080, event=event@entry=0x7fffffffc700, alienWidget=<optimized out>, nativeWidget=0x555559f3b080, buttonDown=buttonDown@entry=0x7ffff6cc43d0 <qt_button_down>, lastMouseReceiver=..., spontaneous=true, onlyDispatchEnterLeave=false) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qapplication.cpp:2619
        graphicsWidget = false
        widgetUnderMouse = <optimized out>
        wasLeaveAfterRelease = <optimized out>
        result = true
#30 0x00007ffff67c1565 in QWidgetWindow::handleMouseEvent(QMouseEvent*) (this=0x555559f3d730, event=0x7fffffffca50) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qwidgetwindow.cpp:683
        translated = {
          <QInputEvent> = {
            <QEvent> = {
              _vptr.QEvent = 0x7ffff64535a0 <vtable for QMouseEvent+16>,
              static staticMetaObject = {
                d = {
                  superdata = {
                    direct = 0x0
                  },
                  stringdata = 0x7ffff5c3f320 <qt_meta_stringdata_QEvent>,
                  data = 0x7ffff5c3ed60 <qt_meta_data_QEvent>,
                  static_metacall = 0x0,
                  relatedMetaObjects = 0x0,
                  extradata = 0x0
                }
              },
              d = 0x0,
              t = 3,
              posted = 0,
              spont = 1,
              m_accept = 1,
              reserved = 8191
            },
            members of QInputEvent:
            modState = {
              i = 0
            },
            ts = 73748715
          },
          members of QMouseEvent:
          l = {
            xp = 41,
            yp = 7
          },
          w = {
            xp = 41,
            yp = 7
          },
          s = {
            xp = 1734,
            yp = 886
          },
          b = Qt::LeftButton,
          mouseState = {
            i = 0
          },
          caps = 0,
          velocity = {
            v = {[0] = 0, [1] = 0}
          }
        }
        contextMenuTrigger = QEvent::MouseButtonPress
        widget = <optimized out>
        mapped = {
          xp = 41,
          yp = 7
        }
        initialPress = <optimized out>
        receiver = 0x555559f3b080
#31 0x00007ffff67c49d8 in QWidgetWindow::event(QEvent*) (this=0x555559f3d730, event=0x7fffffffca50) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qwidgetwindow.cpp:300
#32 0x00007ffff67633fe in QApplicationPrivate::notify_helper(QObject*, QEvent*) (this=this@entry=0x4044800000000000, receiver=receiver@entry=0x555559f3d730, e=0x7fffffffca50) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qapplication.cpp:3637
        consumed = false
        filtered = false
#33 0x00007ffff676acaf in QApplication::notify(QObject*, QEvent*) (this=this@entry=0x7fffffffcff0, receiver=receiver@entry=0x555559f3d730, e=e@entry=0x7fffffffca50) at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qapplication.cpp:3383
        w = <optimized out>
        extra = <optimized out>
        isProxyWidget = <optimized out>
        d = 0x4044800000000000
        res = false
#34 0x00007ffff7aeb79e in KisApplication::notify(QObject*, QEvent*) (this=0x7fffffffcff0, receiver=0x555559f3d730, event=0x7fffffffca50) at /usr/src/debug/media-gfx/krita-5.1.4-r1/krita-5.1.4/libs/ui/KisApplication.cpp:762
        guard = {
          m_info = 0x5555565759a0
        }
        result = true
        info = @0x5555565759a0: {
          eventRecursionCount = 2,
          postponedSynchronizationEvents = std::queue wrapping: std::deque with 0 elements
        }
#35 0x00007ffff5a8b548 in QCoreApplication::notifyInternal2(QObject*, QEvent*) (receiver=0x555559f3d730, event=0x7fffffffca50) at /usr/src/debug/dev-qt/qtcore-5.15.7/qtbase-everywhere-src-5.15.7/src/corelib/kernel/qcoreapplication.cpp:1064
        selfRequired = true
        result = false
        cbdata = {[0] = 0x555559f3d730, [1] = 0x7fffffffca50, [2] = 0x7fffffffc8ef}
        d = <optimized out>
        threadData = 0x555555e6cc80
        scopeLevelCounter = {
          threadData = 0x555555e6cc80
        }
#36 0x00007ffff5f27426 in QGuiApplicationPrivate::processMouseEvent(QWindowSystemInterfacePrivate::MouseEvent*) (e=0x555559eea650) at /usr/src/debug/dev-qt/qtgui-5.15.7-r1/qtbase-everywhere-src-5.15.7/src/gui/kernel/qguiapplication.cpp:2285
        type = QEvent::MouseButtonRelease
        button = <optimized out>
        window = <optimized out>
        positionChanged = <optimized out>
        mouseMove = <optimized out>
        mousePress = <optimized out>
        localPoint = {
          xp = 41,
          yp = 7
        }
        globalPoint = {
          xp = 1734,
          yp = 886
        }
        doubleClick = false
        ev = {
          <QInputEvent> = {
            <QEvent> = {
              _vptr.QEvent = 0x7ffff64535a0 <vtable for QMouseEvent+16>,
              static staticMetaObject = {
                d = {
                  superdata = {
                    direct = 0x0
                  },
                  stringdata = 0x7ffff5c3f320 <qt_meta_stringdata_QEvent>,
                  data = 0x7ffff5c3ed60 <qt_meta_data_QEvent>,
                  static_metacall = 0x0,
                  relatedMetaObjects = 0x0,
                  extradata = 0x0
                }
              },
              d = 0x0,
              t = 3,
              posted = 0,
              spont = 1,
              m_accept = 1,
              reserved = 2755
            },
            members of QInputEvent:
            modState = {
              i = 0
            },
            ts = 73748715
          },
          members of QMouseEvent:
          l = {
            xp = 41,
            yp = 7
          },
          w = {
            xp = 41,
            yp = 7
          },
          s = {
            xp = 1734,
            yp = 886
          },
          b = Qt::LeftButton,
          mouseState = {
            i = 0
          },
          caps = 0,
          velocity = {
            v = {[0] = 0, [1] = 0}
          }
        }
#37 0x00007ffff5f0640b in QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) (flags=flags@entry=...) at /usr/src/debug/dev-qt/qtgui-5.15.7-r1/qtbase-everywhere-src-5.15.7/src/gui/kernel/qwindowsysteminterface.cpp:1169
        event = 0x555559eea650
        nevents = 1
#38 0x00007ffff0515e4a in xcbSourceDispatch(GSource*, GSourceFunc, gpointer) (source=<optimized out>) at /usr/src/debug/dev-qt/qtgui-5.15.7-r1/qtbase-everywhere-src-5.15.7/src/plugins/platforms/xcb/qxcbeventdispatcher.cpp:105
        xcbEventSource = <optimized out>
        flags = {
          i = 36
        }
#39 0x00007ffff3e0c838 in g_main_dispatch (context=0x7fffe8005010) at ../glib-2.74.4/glib/gmain.c:3454
        dispatch = 0x7ffff0515e30 <xcbSourceDispatch(GSource*, GSourceFunc, gpointer)>
        prev_source = 0x0
        begin_time_nsec = 0
        was_in_call = 0
        user_data = 0x0
        callback = 0x0
        cb_funcs = <optimized out>
        cb_data = <optimized out>
        need_destroy = <optimized out>
        source = 0x55555620e840
        current = 0x555556944780
        i = 1
        __func__ = "g_main_dispatch"
#40 g_main_context_dispatch (context=context@entry=0x7fffe8005010) at ../glib-2.74.4/glib/gmain.c:4172
#41 0x00007ffff3e0cad8 in g_main_context_iterate (context=context@entry=0x7fffe8005010, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../glib-2.74.4/glib/gmain.c:4248
        max_priority = 2147483647
        timeout = 525
        some_ready = 1
        nfds = <optimized out>
        allocated_nfds = 4
        fds = 0x55555cf613e0
#42 0x00007ffff3e0cb6c in g_main_context_iteration (context=0x7fffe8005010, may_block=1) at ../glib-2.74.4/glib/gmain.c:4313
        retval = <optimized out>
#43 0x00007ffff5ae06f6 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x5555561b43c0, flags=...) at /usr/src/debug/dev-qt/qtcore-5.15.7/qtbase-everywhere-src-5.15.7/src/corelib/kernel/qeventdispatcher_glib.cpp:423
        d = 0x555555ef5460
        canWait = true
        savedFlags = {
          i = 0
        }
        result = <optimized out>
#44 0x00007ffff5a89f5b in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) (this=this@entry=0x7fffffffcda0, flags=..., flags@entry=...) at /usr/src/debug/dev-qt/qtcore-5.15.7/qtbase-everywhere-src-5.15.7/include/QtCore/../../src/corelib/global/qflags.h:69
        d = 0x5555569884c0
        threadData = <optimized out>
        locker = {
          val = 93825001770360
        }
        app = <optimized out>
#45 0x00007ffff5a92246 in QCoreApplication::exec() () at /usr/src/debug/dev-qt/qtcore-5.15.7/qtbase-everywhere-src-5.15.7/include/QtCore/../../src/corelib/global/qflags.h:121
        threadData = 0x555555e6cc80
        eventLoop = {
          <QObject> = {
            _vptr.QObject = 0x7ffff5d62f08 <vtable for QEventLoop+16>,
            static staticMetaObject = {
              d = {
                superdata = {
                  direct = 0x0
                },
                stringdata = 0x7ffff5c43a20 <qt_meta_stringdata_QObject>,
                data = 0x7ffff5c43900 <qt_meta_data_QObject>,
                static_metacall = 0x7ffff5abe4c0 <QObject::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>,
                relatedMetaObjects = 0x0,
                extradata = 0x0
              }
            },
            d_ptr = {
              d = 0x5555569884c0
            },
            static staticQtMetaObject = {
              d = {
                superdata = {
                  direct = 0x0
                },
                stringdata = 0x7ffff5c469c0 <qt_meta_stringdata_Qt>,
                data = 0x7ffff5c43b40 <qt_meta_data_Qt>,
                static_metacall = 0x0,
                relatedMetaObjects = 0x0,
                extradata = 0x0
              }
            }
          },
          members of QEventLoop:
          static staticMetaObject = {
            d = {
              superdata = {
                direct = 0x7ffff5d5a780 <QObject::staticMetaObject>
              },
              stringdata = 0x7ffff5c3e1c0 <qt_meta_stringdata_QEventLoop>,
              data = 0x7ffff5c3e160 <qt_meta_data_QEventLoop>,
              static_metacall = 0x7ffff5a89c70 <QEventLoop::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>,
              relatedMetaObjects = 0x0,
              extradata = 0x0
            }
          }
        }
        returnCode = <optimized out>
#46 0x00007ffff5f1bcbc in QGuiApplication::exec() () at /usr/src/debug/dev-qt/qtgui-5.15.7-r1/qtbase-everywhere-src-5.15.7/src/gui/kernel/qguiapplication.cpp:1870
#47 0x00007ffff6763375 in QApplication::exec() () at /usr/src/debug/dev-qt/qtwidgets-5.15.7/qtbase-everywhere-src-5.15.7/src/widgets/kernel/qapplication.cpp:2829
#48 0x000055555555d412 in main(int, char**) (argc=<optimized out>, argv=<optimized out>) at /usr/src/debug/media-gfx/krita-5.1.4-r1/krita-5.1.4/krita/main.cc:721
        runningInKDE = false
        key = {
          d = 0x555555e6c630
        }
        configPath = {
          d = 0x555555e6c6e0
        }
        kritarc = {
          <QObject> = {
            _vptr.QObject = 0x7ffff5d614f0 <vtable for QSettings+16>,
            static staticMetaObject = {
              d = {
                superdata = {
                  direct = 0x0
                },
                stringdata = 0x7ffff5c43a20 <qt_meta_stringdata_QObject>,
                data = 0x7ffff5c43900 <qt_meta_data_QObject>,
                static_metacall = 0x7ffff5abe4c0 <QObject::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>,
                relatedMetaObjects = 0x0,
                extradata = 0x0
              }
            },
            d_ptr = {
              d = 0x555555e6c730
            },
            static staticQtMetaObject = {
              d = {
                superdata = {
                  direct = 0x0
                },
                stringdata = 0x7ffff5c469c0 <qt_meta_stringdata_Qt>,
                data = 0x7ffff5c43b40 <qt_meta_data_Qt>,
                static_metacall = 0x0,
                relatedMetaObjects = 0x0,
                extradata = 0x0
              }
            }
          },
          members of QSettings:
          static staticMetaObject = {
            d = {
              superdata = {
                direct = 0x7ffff5d5a780 <QObject::staticMetaObject>
              },
              stringdata = 0x7ffff5c35a60 <qt_meta_stringdata_QSettings>,
              data = 0x7ffff5c35920 <qt_meta_data_QSettings>,
              static_metacall = 0x7ffff5a18fe0 <QSettings::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>,
              relatedMetaObjects = 0x0,
              extradata = 0x0
            }
          }
        }
        enableOpenGLDebug = <optimized out>
        openGLDebugSynchronous = <optimized out>
        logUsage = <optimized out>
        root = {
          d = 0x555556196630
        }
        language = {
          d = 0x5555560d2aa0
        }
        rightToLeft = false
        app = {
          <QtSingleApplication> = {
            <QApplication> = {
              <QGuiApplication> = {
                <QCoreApplication> = {
                  <QObject> = {
                    _vptr.QObject = 0x7ffff7d7a880 <vtable for KisApplication+16>,
                    static staticMetaObject = {
                      d = {
                        superdata = {
                          direct = 0x0
                        },
                        stringdata = 0x7ffff5c43a20 <qt_meta_stringdata_QObject>,
                        data = 0x7ffff5c43900 <qt_meta_data_QObject>,
                        static_metacall = 0x7ffff5abe4c0 <QObject::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>,
                        relatedMetaObjects = 0x0,
                        extradata = 0x0
                      }
                    },
                    d_ptr = {
                      d = 0x555555e81150
                    },
                    static staticQtMetaObject = {
                      d = {
                        superdata = {
                          direct = 0x0
                        },
                        stringdata = 0x7ffff5c469c0 <qt_meta_stringdata_Qt>,
                        data = 0x7ffff5c43b40 <qt_meta_data_Qt>,
                        static_metacall = 0x0,
                        relatedMetaObjects = 0x0,
                        extradata = 0x0
                      }
                    }
                  },
                  members of QCoreApplication:
                  static staticMetaObject = {
                    d = {
                      superdata = {
                        direct = 0x7ffff5d5a780 <QObject::staticMetaObject>
                      },
                      stringdata = 0x7ffff5c3e8a0 <qt_meta_stringdata_QCoreApplication>,
                      data = 0x7ffff5c3e780 <qt_meta_data_QCoreApplication>,
                      static_metacall = 0x7ffff5a8ceb0 <QCoreApplication::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>,
                      relatedMetaObjects = 0x0,
                      extradata = 0x0
                    }
                  },
                  static self = 0x7fffffffcff0
                },
                members of QGuiApplication:
                static staticMetaObject = {
                  d = {
                    superdata = {
                      direct = 0x7ffff5d630a0 <QCoreApplication::staticMetaObject>
                    },
                    stringdata = 0x7ffff6355440 <qt_meta_stringdata_QGuiApplication>,
                    data = 0x7ffff63551c0 <qt_meta_data_QGuiApplication>,
                    static_metacall = 0x7ffff5f1ccf0 <QGuiApplication::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>,
                    relatedMetaObjects = 0x0,
                    extradata = 0x0
                  }
                }
              },
              members of QApplication:
              static staticMetaObject = {
                d = {
                  superdata = {
                    direct = 0x7ffff6452ea0 <QGuiApplication::staticMetaObject>
                  },
                  stringdata = 0x7ffff6b328c0 <qt_meta_stringdata_QApplication>,
                  data = 0x7ffff6b32740 <qt_meta_data_QApplication>,
                  static_metacall = 0x7ffff6767180 <QApplication::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>,
                  relatedMetaObjects = 0x0,
                  extradata = 0x0
                }
              }
            },
            members of QtSingleApplication:
            static staticMetaObject = {
              d = {
                superdata = {
                  direct = 0x7ffff6c958a0 <QApplication::staticMetaObject>
                },
                stringdata = 0x7ffff7bd1a40 <qt_meta_stringdata_QtSingleApplication>,
                data = 0x7ffff7bd1920 <qt_meta_data_QtSingleApplication>,
                static_metacall = 0x7ffff76ba450 <QtSingleApplication::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>,
                relatedMetaObjects = 0x0,
                extradata = 0x0
              }
            },
            firstPeer = -1,
            instances = 0x55555697b3d0,
            pidPeer = 0x555555f44c60,
            actWin = 0x0,
            appId = {
              d = 0x555555e6c630
            },
            block = false
          },
          members of KisApplication:
          static staticMetaObject = {
            d = {
              superdata = {
                direct = 0x7ffff7d9bc80 <QtSingleApplication::staticMetaObject>
              },
              stringdata = 0x7ffff7befce0 <qt_meta_stringdata_KisApplication>,
              data = 0x7ffff7befc00 <qt_meta_data_KisApplication>,
              static_metacall = 0x7ffff76c2410 <KisApplication::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>,
              relatedMetaObjects = 0x0,
              extradata = 0x0
            }
          },
          d = {
            d = 0x55555659dd70
          }
        }
        args = {
          d = {
            d = 0x55555694f650
          }
        }
        state = <optimized out>
>>> f 1
#1  0x00007ffff5a94319 in QMetaObject::cast (this=0x7ffff6c97b40 <QWidgetWindow::staticMetaObject>, obj=0x555559f45e50) at /usr/src/debug/dev-qt/qtcore-5.15.7/qtbase-everywhere-src-5.15.7/src/corelib/kernel/qmetaobject.cpp:389
389         return (obj && obj->metaObject()->inherits(this)) ? obj : nullptr;


STEPS TO REPRODUCE
1. Settings->Docker and enable Last Documents Docker or Comics Manager
2. Try to dock said docker somewhere else

OBSERVED RESULT
SIGSEGV, krita crashes

EXPECTED RESULT
No crash

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Gentoo linux
KDE Plasma Version: not installed
KDE Frameworks Version: 5.101.0
Qt Version: 5.15.7

ADDITIONAL INFORMATION