I have the same problem. Helps that:

Application: Plasma Workspace (plasma-desktop), signal: Segmentation fault
[Current thread is 1 (Thread 0xb614ba30 (LWP 1630))]

Thread 2 (Thread 0xade5bb70 (LWP 1634)):
#0  0x003f6416 in __kernel_vsyscall ()
#1  0x009fade6 in poll () from /lib/libc.so.6
#2  0x02379a1b in g_poll () from /lib/libglib-2.0.so.0
#3  0x0236c43c in ?? () from /lib/libglib-2.0.so.0
#4  0x0236c848 in g_main_context_iteration () from /lib/libglib-2.0.so.0
#5  0x06d1159f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#6  0x06ce1609 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#7  0x06ce1a8a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#8  0x06bddb7e in QThread::exec() () from /usr/lib/libQtCore.so.4
#9  0x06cc035b in ?? () from /usr/lib/libQtCore.so.4
#10 0x06be0df9 in ?? () from /usr/lib/libQtCore.so.4
#11 0x07d7cba8 in ?? () from /usr/lib/nvidia-current/libGL.so.1

Thread 1 (Thread 0xb614ba30 (LWP 1630)):
[KCrash Handler]
#7  0x02ee69a2 in findActionItemForAction (this=0x9b50b20, event=0xbfca4df8) at /build/buildd/plasma-widget-message-indicator-0.5.6/src/listenermodel.cpp:189
#8  removeAction (this=0x9b50b20, event=0xbfca4df8) at /build/buildd/plasma-widget-message-indicator-0.5.6/src/listenermodel.cpp:177
#9  ServerItem::eventFilter (this=0x9b50b20, event=0xbfca4df8) at /build/buildd/plasma-widget-message-indicator-0.5.6/src/listenermodel.cpp:150
#10 0x06ce229a in QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject*, QEvent*) () from /usr/lib/libQtCore.so.4
#11 0x01478fb9 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#12 0x0147f0e9 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#13 0x0116e68a in KApplication::notify(QObject*, QEvent*) () from /usr/lib/libkdeui.so.5
#14 0x06ce2b3b in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQtCore.so.4
#15 0x014cc58a in QWidget::removeAction(QAction*) () from /usr/lib/libQtGui.so.4
#16 0x0193dce8 in QMenu::clear() () from /usr/lib/libQtGui.so.4
#17 0x0437749b in DBusMenuImporter::GetChildrenCallback(int, QDBusPendingCallWatcher*) () from /usr/lib/libdbusmenu-qt.so.2
#18 0x0437647e in DBusMenuImporter::dispatch(QDBusPendingCallWatcher*) () from /usr/lib/libdbusmenu-qt.so.2
#19 0x0437aeaf in DBusMenuImporter::qt_metacall(QMetaObject::Call, int, void**) () from /usr/lib/libdbusmenu-qt.so.2
#20 0x06ce88ca in QMetaObject::metacall(QObject*, QMetaObject::Call, int, void**) () from /usr/lib/libQtCore.so.4
#21 0x06cfb6ad in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/libQtCore.so.4
#22 0x00af49c3 in QDBusPendingCallWatcher::finished(QDBusPendingCallWatcher*) () from /usr/lib/libQtDBus.so.4
#23 0x00af4a5a in QDBusPendingCallWatcher::qt_metacall(QMetaObject::Call, int, void**) () from /usr/lib/libQtDBus.so.4
#24 0x06ce88ca in QMetaObject::metacall(QObject*, QMetaObject::Call, int, void**) () from /usr/lib/libQtCore.so.4
#25 0x06cf3df6 in QMetaCallEvent::placeMetaCall(QObject*) () from /usr/lib/libQtCore.so.4
#26 0x06cf56a2 in QObject::event(QEvent*) () from /usr/lib/libQtCore.so.4
#27 0x01478fdc in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#28 0x0147f04e in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#29 0x0116e68a in KApplication::notify(QObject*, QEvent*) () from /usr/lib/libkdeui.so.5
#30 0x06ce2b3b in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQtCore.so.4
#31 0x06ce5d8b in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/libQtCore.so.4
#32 0x06ce5f4d in QCoreApplication::sendPostedEvents(QObject*, int) () from /usr/lib/libQtCore.so.4
#33 0x06d11a74 in ?? () from /usr/lib/libQtCore.so.4
#34 0x02368855 in g_main_context_dispatch () from /lib/libglib-2.0.so.0
#35 0x0236c668 in ?? () from /lib/libglib-2.0.so.0
#36 0x0236c848 in g_main_context_iteration () from /lib/libglib-2.0.so.0
#37 0x06d11565 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#38 0x0153abe5 in ?? () from /usr/lib/libQtGui.so.4
#39 0x06ce1609 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#40 0x06ce1a8a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#41 0x06ce600f in QCoreApplication::exec() () from /usr/lib/libQtCore.so.4
#42 0x01477e07 in QApplication::exec() () from /usr/lib/libQtGui.so.4
#43 0x0045686e in kdemain () from /usr/lib/kde4/libkdeinit/libkdeinit4_plasma-desktop.so
#44 0x080485bb in _start ()