Plasmashell just entirely froze for the 2nd time within less than an hour. Both time, this happened shortly after I used the shortcut "Win+D" to trigger "Show Desktop", and then interacted with the folder view on the desktop.

Reproducible: Sometimes

Steps to Reproduce:
1. Trigger "Show Desktop"
2. Interact with a folder widget on the desktop

Actual Results:  
Plasma entirely freezes. The panel stops updating and reacting. I have to "killall plasmashell" to get back to a working desktop.

Expected Results:  
Plasma should never freeze

I attached gdb, here's what I saw:

#0  0x00007fd4c71f4e4d in poll () at ../sysdeps/unix/syscall-template.S:84
#1  0x00007fd4c3d35dff in ?? () from /lib/x86_64-linux-gnu/libdbus-1.so.3
#2  0x00007fd4c3d34a6e in ?? () from /lib/x86_64-linux-gnu/libdbus-1.so.3
#3  0x00007fd4c3d1d6c4 in ?? () from /lib/x86_64-linux-gnu/libdbus-1.so.3
#4  0x00007fd4c3d1e1bc in ?? () from /lib/x86_64-linux-gnu/libdbus-1.so.3
#5  0x00007fd4c3d1e67a in dbus_connection_send_with_reply_and_block () from /lib/x86_64-linux-gnu/libdbus-1.so.3
#6  0x00007fd4ccc203a0 in q_dbus_connection_send_with_reply_and_block (error=<optimized out>, timeout_milliseconds=2147483647, message=0x626b490, connection=<optimized out>)
    at qdbus_symbols_p.h:208
#7  QDBusConnectionPrivate::sendWithReply (this=0x12898d0, message=..., sendMode=<optimized out>, timeout=2147483647) at qdbusintegrator.cpp:2044
#8  0x00007fd4ccc0d88b in QDBusConnection::call (this=0x7ffd11c03c20, message=..., mode=<optimized out>, timeout=<optimized out>) at qdbusconnection.cpp:564
#9  0x00007fd4c9792ccd in KToolInvocation::startServiceInternal(char const*, QString const&, QStringList const&, QString*, QString*, int*, QByteArray const&, bool, QString const&) ()
   from /usr/lib/x86_64-linux-gnu/libKF5Service.so.5
#10 0x00007fd4c97936cc in KToolInvocation::startServiceByDesktopPath(QString const&, QStringList const&, QString*, QString*, int*, QByteArray const&, bool) ()
   from /usr/lib/x86_64-linux-gnu/libKF5Service.so.5
#11 0x00007fd4c5ae9e20 in KRun::runService(KService const&, QList<QUrl> const&, QWidget*, bool, QString const&, QByteArray const&) () from /usr/lib/x86_64-linux-gnu/libKF5KIOWidgets.so.5
#12 0x00007fd4c5ac431e in ?? () from /usr/lib/x86_64-linux-gnu/libKF5KIOWidgets.so.5
#13 0x00007fd4c5b22034 in ?? () from /usr/lib/x86_64-linux-gnu/libKF5KIOWidgets.so.5
#14 0x00007fd4c7ae8f8a in QMetaObject::activate (sender=0x6003220, signalOffset=<optimized out>, local_signal_index=local_signal_index@entry=0, argv=argv@entry=0x7ffd11c040c0)
    at kernel/qobject.cpp:3713
#15 0x00007fd4c7ae9797 in QMetaObject::activate (sender=<optimized out>, m=m@entry=0x7fd4c8abefe0 <QActionGroup::staticMetaObject>, local_signal_index=local_signal_index@entry=0, 
    argv=argv@entry=0x7ffd11c040c0) at kernel/qobject.cpp:3578
#16 0x00007fd4c85b68ff in QActionGroup::triggered (this=<optimized out>, _t1=0x61ee530) at .moc/moc_qactiongroup.cpp:239
#17 0x00007fd4c85b6b38 in QActionGroupPrivate::_q_actionTriggered (this=<optimized out>) at kernel/qactiongroup.cpp:85
#18 0x00007fd4c85b7579 in QActionGroup::qt_static_metacall (_o=_o@entry=0x6003220, _c=_c@entry=QMetaObject::InvokeMetaMethod, _id=_id@entry=6, _a=_a@entry=0x7ffd11c04240)
    at .moc/moc_qactiongroup.cpp:117
#19 0x00007fd4c7ae8f8a in QMetaObject::activate (sender=sender@entry=0x61ee530, signalOffset=<optimized out>, local_signal_index=local_signal_index@entry=1, argv=argv@entry=0x7ffd11c04240)
    at kernel/qobject.cpp:3713
#20 0x00007fd4c7ae9797 in QMetaObject::activate (sender=sender@entry=0x61ee530, m=m@entry=0x7fd4c8abef00 <QAction::staticMetaObject>, local_signal_index=local_signal_index@entry=1, 
    argv=argv@entry=0x7ffd11c04240) at kernel/qobject.cpp:3578
#21 0x00007fd4c85b33b2 in QAction::triggered (this=this@entry=0x61ee530, _t1=false) at .moc/moc_qaction.cpp:365
#22 0x00007fd4c85b5838 in QAction::activate (this=0x61ee530, event=<optimized out>) at kernel/qaction.cpp:1162
#23 0x00007fd4c8737cd2 in QMenuPrivate::activateCausedStack (this=this@entry=0x5e51370, causedStack=..., action=action@entry=0x61ee530, action_e=action_e@entry=QAction::Trigger, 
    self=self@entry=true) at widgets/qmenu.cpp:1130
#24 0x00007fd4c873df6c in QMenuPrivate::activateAction (this=this@entry=0x5e51370, action=action@entry=0x61ee530, action_e=action_e@entry=QAction::Trigger, self=self@entry=true)
    at widgets/qmenu.cpp:1207
#25 0x00007fd4c8741ee0 in QMenu::mouseReleaseEvent (this=<optimized out>, e=0x7ffd11c04880) at widgets/qmenu.cpp:2540
#26 0x00007fd4c85fff28 in QWidget::event (this=this@entry=0x4c82d70, event=event@entry=0x7ffd11c04880) at kernel/qwidget.cpp:9044
#27 0x00007fd4c8742923 in QMenu::event (this=0x4c82d70, e=0x7ffd11c04880) at widgets/qmenu.cpp:2654
#28 0x00007fd4c85bcffc in QApplicationPrivate::notify_helper (this=this@entry=0x123d8d0, receiver=receiver@entry=0x4c82d70, e=e@entry=0x7ffd11c04880) at kernel/qapplication.cpp:3716
#29 0x00007fd4c85c2bb9 in QApplication::notify (this=<optimized out>, receiver=0x4c82d70, e=0x7ffd11c04880) at kernel/qapplication.cpp:3276
#30 0x00007fd4c7aba5ab in QCoreApplication::notifyInternal (this=0x7ffd11c05170, receiver=receiver@entry=0x4c82d70, event=event@entry=0x7ffd11c04880) at kernel/qcoreapplication.cpp:965
#31 0x00007fd4c85c1ad2 in QCoreApplication::sendSpontaneousEvent (event=0x7ffd11c04880, receiver=0x4c82d70) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:227
#32 QApplicationPrivate::sendMouseEvent (receiver=receiver@entry=0x4c82d70, event=event@entry=0x7ffd11c04880, alienWidget=alienWidget@entry=0x0, nativeWidget=0x4c82d70, 
    buttonDown=buttonDown@entry=0x7fd4c8aedb20 <qt_button_down>, lastMouseReceiver=..., spontaneous=true) at kernel/qapplication.cpp:2770
#33 0x00007fd4c861a7dd in QWidgetWindow::handleMouseEvent (this=this@entry=0x5ff4e50, event=event@entry=0x7ffd11c04c90) at kernel/qwidgetwindow.cpp:452
#34 0x00007fd4c861ca3b in QWidgetWindow::event (this=0x5ff4e50, event=0x7ffd11c04c90) at kernel/qwidgetwindow.cpp:210
#35 0x00007fd4c85bcffc in QApplicationPrivate::notify_helper (this=this@entry=0x123d8d0, receiver=receiver@entry=0x5ff4e50, e=e@entry=0x7ffd11c04c90) at kernel/qapplication.cpp:3716
#36 0x00007fd4c85c24b6 in QApplication::notify (this=0x7ffd11c05170, receiver=0x5ff4e50, e=0x7ffd11c04c90) at kernel/qapplication.cpp:3499
#37 0x00007fd4c7aba5ab in QCoreApplication::notifyInternal (this=0x7ffd11c05170, receiver=receiver@entry=0x5ff4e50, event=event@entry=0x7ffd11c04c90) at kernel/qcoreapplication.cpp:965
#38 0x00007fd4c7dfc101 in QCoreApplication::sendSpontaneousEvent (event=0x7ffd11c04c90, receiver=0x5ff4e50) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:227
#39 QGuiApplicationPrivate::processMouseEvent (e=0x4540c00) at kernel/qguiapplication.cpp:1789
#40 0x00007fd4c7dfddc5 in QGuiApplicationPrivate::processWindowSystemEvent (e=e@entry=0x4540c00) at kernel/qguiapplication.cpp:1581
#41 0x00007fd4c7de1df8 in QWindowSystemInterface::sendWindowSystemEvents (flags=...) at kernel/qwindowsysteminterface.cpp:625
#42 0x00007fd4b8cde0b0 in userEventSourceDispatch (source=<optimized out>) at eventdispatchers/qeventdispatcher_glib.cpp:70
#43 0x00007fd4c3fa2fd7 in g_main_context_dispatch () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#44 0x00007fd4c3fa3230 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#45 0x00007fd4c3fa32dc in g_main_context_iteration () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#46 0x00007fd4c7b10a3f in QEventDispatcherGlib::processEvents (this=0x127ea90, flags=...) at kernel/qeventdispatcher_glib.cpp:418
#47 0x00007fd4c7ab7d6a in QEventLoop::exec (this=this@entry=0x7ffd11c05010, flags=..., flags@entry=...) at kernel/qeventloop.cpp:204
#48 0x00007fd4c7abfe0c in QCoreApplication::exec () at kernel/qcoreapplication.cpp:1229
#49 0x0000000000432cc4 in main ()

It seems that Plasma is using blocking calls in the main thread. I don't think I need to say more...