Similar bug 268469 (which was fixed back in 2013, but appears to be back now): Umbrello crashes as soon as you try to add a class to a package.

Reproducible: Always

Steps to Reproduce:
1. create a new document
2. add a class "MyClass" and a package "MyPackage" to the document
3. edit the "MyClass" and update its package path to "MyPackage"
4. click OK or Apply
5. Umbrello immediately crashes

Actual Results:  
Umbrello crashes

Expected Results:  
Class gets added to package without crashing

Unfortunately, Ubuntu does not provide a package for debugging symbols (I think?), but this is the stack trace without details:

Application: Umbrello UML Modeller (umbrello), signal: Segmentation fault
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[KCrash Handler]
#6  QAbstractButton::isChecked (this=0x0) at widgets/qabstractbutton.cpp:774
#7  0x00000000004f564d in ?? ()
#8  0x00000000004c4f23 in ?? ()
#9  0x00000000004c4f79 in ?? ()
#10 0x00007f85b2d1419c in QMetaObject::activate (sender=0x1f59030, m=<optimized out>, local_signal_index=<optimized out>, argv=0x0) at kernel/qobject.cpp:3567
#11 0x00007f85b2d1419c in QMetaObject::activate (sender=0x1b12af0, m=<optimized out>, local_signal_index=<optimized out>, argv=0x0) at kernel/qobject.cpp:3567
#12 0x00007f85b486ecb8 in KDialog::slotButtonClicked(int) () from /usr/lib/libkdeui.so.5
#13 0x00007f85b487082f in ?? () from /usr/lib/libkdeui.so.5
#14 0x00007f85b2d1419c in QMetaObject::activate (sender=sender@entry=0x1f578e0, m=m@entry=0x7f85b30624c0 <QSignalMapper::staticMetaObject>, local_signal_index=local_signal_index@entry=0, argv=argv@entry=0x7ffee278e240) at kernel/qobject.cpp:3567
#15 0x00007f85b2d1be0e in QSignalMapper::mapped (this=this@entry=0x1f578e0, _t1=4) at .moc/release-shared/moc_qsignalmapper.cpp:114
#16 0x00007f85b2d1bf96 in QSignalMapper::map (this=0x1f578e0, sender=0x1f42330) at kernel/qsignalmapper.cpp:266
#17 0x00007f85b2d1419c in QMetaObject::activate (sender=sender@entry=0x1f42330, m=m@entry=0x7f85b3f948e0 <QAbstractButton::staticMetaObject>, local_signal_index=local_signal_index@entry=2, argv=argv@entry=0x7ffee278e3c0) at kernel/qobject.cpp:3567
#18 0x00007f85b3b112f2 in QAbstractButton::clicked (this=this@entry=0x1f42330, _t1=false) at .moc/release-shared/moc_qabstractbutton.cpp:219
#19 0x00007f85b384e533 in QAbstractButtonPrivate::emitClicked (this=this@entry=0x1f6d0c0) at widgets/qabstractbutton.cpp:548
#20 0x00007f85b384f8e4 in QAbstractButtonPrivate::click (this=this@entry=0x1f6d0c0) at widgets/qabstractbutton.cpp:541
#21 0x00007f85b384f9f4 in QAbstractButton::mouseReleaseEvent (this=0x1f42330, e=0x7ffee278e920) at widgets/qabstractbutton.cpp:1123
#22 0x00007f85b34cbdc8 in QWidget::event (this=0x1f42330, event=0x7ffee278e920) at kernel/qwidget.cpp:8775
#23 0x00007f85b34789bc in QApplicationPrivate::notify_helper (this=this@entry=0x172ba70, receiver=receiver@entry=0x1f42330, e=e@entry=0x7ffee278e920) at kernel/qapplication.cpp:4570
#24 0x00007f85b347f63f in QApplication::notify (this=<optimized out>, receiver=0x1f42330, e=0x7ffee278e920) at kernel/qapplication.cpp:4113
#25 0x00007f85b491ba2a in KApplication::notify(QObject*, QEvent*) () from /usr/lib/libkdeui.so.5
#26 0x00007f85b2cff17d in QCoreApplication::notifyInternal (this=0x7ffee2790300, receiver=receiver@entry=0x1f42330, event=event@entry=0x7ffee278e920) at kernel/qcoreapplication.cpp:955
#27 0x00007f85b347ec9f in sendEvent (event=<optimized out>, receiver=<optimized out>) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:231
#28 QApplicationPrivate::sendMouseEvent (receiver=receiver@entry=0x1f42330, event=event@entry=0x7ffee278e920, alienWidget=alienWidget@entry=0x1f42330, nativeWidget=nativeWidget@entry=0x1b12af0, buttonDown=buttonDown@entry=0x7f85b3fa6578 <qt_button_down>, lastMouseReceiver=..., spontaneous=true) at kernel/qapplication.cpp:3178
#29 0x00007f85b34f89a2 in QETWidget::translateMouseEvent (this=this@entry=0x1b12af0, event=event@entry=0x7ffee278ec80) at kernel/qapplication_x11.cpp:4632
#30 0x00007f85b34f824c in QApplication::x11ProcessEvent (this=0x7ffee2790300, event=event@entry=0x7ffee278ec80) at kernel/qapplication_x11.cpp:3626
#31 0x00007f85b3520ba2 in x11EventSourceDispatch (s=0x17134d0, callback=0x0, user_data=0x0) at kernel/qguieventdispatcher_glib.cpp:146
#32 0x00007f85ae5c8c3d in g_main_context_dispatch () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#33 0x00007f85ae5c8f20 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#34 0x00007f85ae5c8fcc in g_main_context_iteration () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#35 0x00007f85b2d2e82e in QEventDispatcherGlib::processEvents (this=0x16f1ae0, flags=...) at kernel/qeventdispatcher_glib.cpp:452
#36 0x00007f85b3520c66 in QGuiEventDispatcherGlib::processEvents (this=<optimized out>, flags=...) at kernel/qguieventdispatcher_glib.cpp:204
#37 0x00007f85b2cfdcd1 in QEventLoop::processEvents (this=this@entry=0x7ffee278f070, flags=...) at kernel/qeventloop.cpp:149
#38 0x00007f85b2cfe035 in QEventLoop::exec (this=this@entry=0x7ffee278f070, flags=...) at kernel/qeventloop.cpp:204
#39 0x00007f85b3952d5c in QDialog::exec (this=0x1b12af0) at dialogs/qdialog.cpp:562
#40 0x000000000066dd2c in ?? ()
#41 0x0000000000673591 in ?? ()
#42 0x00000000006f1e50 in ?? ()
#43 0x0000000000487bcb in ?? ()
#44 0x00007f85b3aa3e98 in QGraphicsScene::event (this=0x1ef85d0, event=0x7ffee278f4f0) at graphicsview/qgraphicsscene.cpp:3461
#45 0x00007f85b34789bc in QApplicationPrivate::notify_helper (this=this@entry=0x172ba70, receiver=receiver@entry=0x1ef85d0, e=e@entry=0x7ffee278f4f0) at kernel/qapplication.cpp:4570
#46 0x00007f85b347f4d8 in QApplication::notify (this=0x7ffee2790300, receiver=0x1ef85d0, e=0x7ffee278f4f0) at kernel/qapplication.cpp:4356
#47 0x00007f85b491ba2a in KApplication::notify(QObject*, QEvent*) () from /usr/lib/libkdeui.so.5
#48 0x00007f85b2cff17d in QCoreApplication::notifyInternal (this=0x7ffee2790300, receiver=0x1ef85d0, event=event@entry=0x7ffee278f4f0) at kernel/qcoreapplication.cpp:955
#49 0x00007f85b3476e26 in sendSpontaneousEvent (event=event@entry=0x7ffee278f4f0, receiver=<optimized out>) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:234
#50 qt_sendSpontaneousEvent (receiver=<optimized out>, event=event@entry=0x7ffee278f4f0) at kernel/qapplication.cpp:5568
#51 0x00007f85b3abb50f in QGraphicsView::mouseDoubleClickEvent (this=0x1ee2040, event=0x7ffee278fae0) at graphicsview/qgraphicsview.cpp:3122
#52 0x00007f85b34cc927 in QWidget::event (this=0x1ee2040, event=0x7ffee278fae0) at kernel/qwidget.cpp:8393
#53 0x00007f85b389260e in QFrame::event (this=0x1ee2040, e=0x7ffee278fae0) at widgets/qframe.cpp:557
#54 0x00007f85b3abc6a1 in QGraphicsView::viewportEvent (this=0x1ee2040, event=0x7ffee278fae0) at graphicsview/qgraphicsview.cpp:2866
#55 0x00007f85b2cff2e6 in QCoreApplicationPrivate::sendThroughObjectEventFilters (this=this@entry=0x172ba70, receiver=receiver@entry=0x1ef8100, event=event@entry=0x7ffee278fae0) at kernel/qcoreapplication.cpp:1065
#56 0x00007f85b347899c in QApplicationPrivate::notify_helper (this=this@entry=0x172ba70, receiver=receiver@entry=0x1ef8100, e=e@entry=0x7ffee278fae0) at kernel/qapplication.cpp:4566
#57 0x00007f85b347f63f in QApplication::notify (this=<optimized out>, receiver=0x1ef8100, e=0x7ffee278fae0) at kernel/qapplication.cpp:4113
#58 0x00007f85b491ba2a in KApplication::notify(QObject*, QEvent*) () from /usr/lib/libkdeui.so.5
#59 0x00007f85b2cff17d in QCoreApplication::notifyInternal (this=0x7ffee2790300, receiver=receiver@entry=0x1ef8100, event=event@entry=0x7ffee278fae0) at kernel/qcoreapplication.cpp:955
#60 0x00007f85b347ec9f in sendEvent (event=<optimized out>, receiver=<optimized out>) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:231
#61 QApplicationPrivate::sendMouseEvent (receiver=receiver@entry=0x1ef8100, event=event@entry=0x7ffee278fae0, alienWidget=alienWidget@entry=0x1ef8100, nativeWidget=nativeWidget@entry=0x1dab410, buttonDown=buttonDown@entry=0x7f85b3fa6578 <qt_button_down>, lastMouseReceiver=..., spontaneous=true) at kernel/qapplication.cpp:3178
#62 0x00007f85b34f89a2 in QETWidget::translateMouseEvent (this=this@entry=0x1dab410, event=event@entry=0x7ffee278fe40) at kernel/qapplication_x11.cpp:4632
#63 0x00007f85b34f824c in QApplication::x11ProcessEvent (this=0x7ffee2790300, event=event@entry=0x7ffee278fe40) at kernel/qapplication_x11.cpp:3626
#64 0x00007f85b3520ba2 in x11EventSourceDispatch (s=0x17134d0, callback=0x0, user_data=0x0) at kernel/qguieventdispatcher_glib.cpp:146
#65 0x00007f85ae5c8c3d in g_main_context_dispatch () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#66 0x00007f85ae5c8f20 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#67 0x00007f85ae5c8fcc in g_main_context_iteration () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#68 0x00007f85b2d2e80e in QEventDispatcherGlib::processEvents (this=0x16f1ae0, flags=...) at kernel/qeventdispatcher_glib.cpp:450
#69 0x00007f85b3520c66 in QGuiEventDispatcherGlib::processEvents (this=<optimized out>, flags=...) at kernel/qguieventdispatcher_glib.cpp:204
#70 0x00007f85b2cfdcd1 in QEventLoop::processEvents (this=this@entry=0x7ffee2790220, flags=...) at kernel/qeventloop.cpp:149
#71 0x00007f85b2cfe035 in QEventLoop::exec (this=this@entry=0x7ffee2790220, flags=...) at kernel/qeventloop.cpp:204
#72 0x00007f85b2d03ab9 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:1227
#73 0x000000000043587d in ?? ()
#74 0x00007f85b2145a40 in __libc_start_main (main=0x434ee0, argc=1, argv=0x7ffee2790468, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7ffee2790458) at libc-start.c:289
#75 0x0000000000447c69 in _start ()