This is probably already fixed in KDE4.2 as the systemtray + notifications were reworked.

Anyways. If you can reproduce the crash at will, may you read http://techbase.kde.org/Development/Tutorials/Debugging/How_to_create_useful_crash_reports and post a complete backtrace here? Thanks :)

Just happened here, 4.2 branch, r931673:

#6  0xffffe424 in __kernel_vsyscall ()
#7  0xb626bc00 in raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
#8  0xb626d668 in abort () at abort.c:88
#9  0xb6483b88 in __gnu_cxx::__verbose_terminate_handler () from /usr/lib/libstdc++.so.6
#10 0xb6481495 in ?? () from /usr/lib/libstdc++.so.6
#11 0xb64814d2 in std::terminate () from /usr/lib/libstdc++.so.6
#12 0xb6482745 in __cxa_pure_virtual () from /usr/lib/libstdc++.so.6
#13 0xb6dd5d09 in QGraphicsItem::sceneBoundingRect (this=0x9f76a98) at graphicsview/qgraphicsitem.cpp:2650
#14 0xb6ded8ae in QGraphicsScenePrivate::estimateItemsInRect (this=0x905dd00, rect=@0xbff9c0d8) at graphicsview/qgraphicsscene.cpp:355
#15 0xb6e098eb in QGraphicsViewPrivate::itemsInArea (this=0x97c4580, path=@0xbff9c200, mode=Qt::IntersectsItemShape) at graphicsview/qgraphicsview.cpp:1763
#16 0xb6e0a263 in QGraphicsView::items (this=0x97c44e0, pos=@0xbff9c308) at graphicsview/qgraphicsview.cpp:1822
#17 0xb6e0a374 in QGraphicsView::itemAt (this=0x6, pos=@0xbff9c308) at graphicsview/qgraphicsview.cpp:1929
#18 0xb6dddb2c in QGraphicsItem::unsetCursor (this=0x9f79ba0) at graphicsview/qgraphicsitem.cpp:1363
#19 0xb6e1f3f5 in QGraphicsProxyWidgetPrivate::setWidget_helper (this=0x9f7aed8, newWidget=0x0, autoShow=true) at graphicsview/qgraphicsproxywidget.cpp:575
#20 0xb6e1f97f in QGraphicsProxyWidget::setWidget (this=0x9f79b98, widget=0x0) at graphicsview/qgraphicsproxywidget.cpp:560
#21 0xb6e1fb26 in ~QGraphicsProxyWidget (this=0x9f79b98) at graphicsview/qgraphicsproxywidget.cpp:529
#22 0xb7e6f738 in ~PushButton (this=0x9f79b98) at /home/maksim/kde42/src/kdelibs/plasma/widgets/pushbutton.cpp:161
#23 0xb6dd9adb in ~QGraphicsItem (this=0x9f76a98) at graphicsview/qgraphicsitem.cpp:815
#24 0xb6e10b02 in ~QGraphicsWidget (this=0x9f76a90) at graphicsview/qgraphicswidget.cpp:220
#25 0xa8d9078f in NotificationWidgetPrivate::completeDetach (this=0x9f1cf58) at /home/maksim/kde42/src/kdebase/workspace/plasma/applets/systemtray/ui/notificationwidget.cpp:148
#26 0xa8d90820 in NotificationWidgetPrivate::destroy (this=0x9f1cf58) at /home/maksim/kde42/src/kdebase/workspace/plasma/applets/systemtray/ui/notificationwidget.cpp:219
#27 0xa8d910a0 in NotificationWidget::qt_metacall (this=0x9f76848, _c=QMetaObject::InvokeMetaMethod, _id=1, _a=0xbff9c62c)
    at /home/maksim/kde42/build/kdebase/workspace/plasma/applets/systemtray/notificationwidget.moc:68
#28 0xb662963a in QMetaObject::activate (sender=0x9f72890, from_signal_index=6, to_signal_index=7, argv=0xbff9c62c) at kernel/qobject.cpp:3013
#29 0xb6629930 in QMetaObject::activate (sender=0x9f72890, m=0xa8d993bc, from_local_signal_index=2, to_local_signal_index=3, argv=0xbff9c62c) at kernel/qobject.cpp:3106
#30 0xa8d7412b in SystemTray::Notification::destroyed (this=0x9f72890, _t1=0x9f72890) at /home/maksim/kde42/build/kdebase/workspace/plasma/applets/systemtray/notification.moc:96
#31 0xa8d747f1 in ~Notification (this=0x9f72890) at /home/maksim/kde42/src/kdebase/workspace/plasma/applets/systemtray/core/notification.cpp:62
#32 0xa8d83367 in ~DBusNotification (this=0x9f72890) at /home/maksim/kde42/src/kdebase/workspace/plasma/applets/systemtray/protocols/notifications/dbusnotification.cpp:38
#33 0xb662471c in qDeleteInEventHandler (o=0x6) at kernel/qobject.cpp:3644
#34 0xb6626103 in QObject::event (this=0x9f72890, e=0x9f72878) at kernel/qobject.cpp:1124
#35 0xb68d2bdc in QApplicationPrivate::notify_helper (this=0x9051078, receiver=0x9f72890, e=0x9f72878) at kernel/qapplication.cpp:3800
#36 0xb68d8fee in QApplication::notify (this=0x9037fc0, receiver=0x9f72890, e=0x9f72878) at kernel/qapplication.cpp:3392
#37 0xb763d659 in KApplication::notify (this=0x9037fc0, receiver=0x9f72890, event=0x9f72878) at /home/maksim/kde42/src/kdelibs/kdeui/kernel/kapplication.cpp:307
#38 0xb6617d21 in QCoreApplication::notifyInternal (this=0x9037fc0, receiver=0x9f72890, event=0x9f72878) at kernel/qcoreapplication.cpp:587
#39 0xb6618679 in QCoreApplicationPrivate::sendPostedEvents (receiver=0x0, event_type=0, data=0x901f808) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:215
#40 0xb661880d in QCoreApplication::sendPostedEvents (receiver=0x0, event_type=0) at kernel/qcoreapplication.cpp:1095
#41 0xb663e9ef in postEventSourceDispatch (s=0x905fd00) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:220
#42 0xb548cc8a in IA__g_main_context_dispatch (context=0x90532b8) at gmain.c:1814
#43 0xb54902f4 in g_main_context_iterate (context=0x90532b8, block=1, dispatch=1, self=0x90598d8) at gmain.c:2448
#44 0xb549047f in IA__g_main_context_iteration (context=0x90532b8, may_block=1) at gmain.c:2511
#45 0xb663e648 in QEventDispatcherGlib::processEvents (this=0x905a3b8, flags={i = -1074148296}) at kernel/qeventdispatcher_glib.cpp:325
#46 0xb695c595 in QGuiEventDispatcherGlib::processEvents (this=0x905a3b8, flags={i = -1074148248}) at kernel/qguieventdispatcher_glib.cpp:204
#47 0xb661648a in QEventLoop::processEvents (this=0xbff9ccd0, flags={i = -1074148184}) at kernel/qeventloop.cpp:149
#48 0xb661664a in QEventLoop::exec (this=0xbff9ccd0, flags={i = -1074148136}) at kernel/qeventloop.cpp:196
#49 0xb66188cd in QCoreApplication::exec () at kernel/qcoreapplication.cpp:849
#50 0xb68d2a57 in QApplication::exec () at kernel/qapplication.cpp:3330
#51 0xb7f42fe7 in kdemain (argc=1, argv=0xbff9ce94) at /home/maksim/kde42/src/kdebase/workspace/plasma/shells/desktop/main.cpp:54
#52 0x08048742 in main (argc=) at /home/maksim/kde42/build/kdebase/workspace/plasma/shells/desktop/plasma_qgv_dummy.cpp:3

Seems easily reproducible to me --- just gett an incoming message in kopete, click a button to view it an boom.

This bug still affects KDE 4.2. Consistently, whenever kopete sends a "User is Online" message to Plasma, and I interact with it (in any way), plasma goes bye bye.

Please wait a minute or two till someone comes online and I can give you a backtrace.

(gdb) bt                                 
#0  0x001b0416 in __kernel_vsyscall ()   
#1  0x00760450 in raise () from /lib/libc.so.6
#2  0x00761e18 in abort () from /lib/libc.so.6
#3  0x04f1cc48 in __gnu_cxx::__verbose_terminate_handler () from /usr/lib/libstdc++.so.6
#4  0x04f1ab35 in ?? () from /usr/lib/libstdc++.so.6                                    
#5  0x04f1ab72 in std::terminate () from /usr/lib/libstdc++.so.6                        
#6  0x04f1b805 in __cxa_pure_virtual () from /usr/lib/libstdc++.so.6                    
#7  0x05e0d3f9 in QGraphicsItem::sceneBoundingRect () from /usr/lib/libQtGui.so.4       
#8  0x05e2fd76 in ?? () from /usr/lib/libQtGui.so.4                                     
#9  0x05e4711b in ?? () from /usr/lib/libQtGui.so.4                                     
#10 0x05e47c56 in QGraphicsView::items () from /usr/lib/libQtGui.so.4                   
#11 0x05e47da2 in QGraphicsView::itemAt () from /usr/lib/libQtGui.so.4                  
#12 0x05e166ee in QGraphicsItem::unsetCursor () from /usr/lib/libQtGui.so.4             
#13 0x05e5e505 in ?? () from /usr/lib/libQtGui.so.4                                     
#14 0x05e5ea83 in QGraphicsProxyWidget::setWidget () from /usr/lib/libQtGui.so.4        
#15 0x05e5ec46 in QGraphicsProxyWidget::~QGraphicsProxyWidget () from /usr/lib/libQtGui.so.4
#16 0x06b584ec in Plasma::PushButton::~PushButton () from /usr/lib/libplasma.so.3           
#17 0x05e12d78 in QGraphicsItem::~QGraphicsItem () from /usr/lib/libQtGui.so.4              
#18 0x05e4e842 in QGraphicsWidget::~QGraphicsWidget () from /usr/lib/libQtGui.so.4          
#19 0x00aebfe8 in ?? () from /usr/lib/kde4/plasma_applet_systemtray.so                      
---Type <return> to continue, or q <return> to quit---
#20 0x00aec0cc in ?? () from /usr/lib/kde4/plasma_applet_systemtray.so
#21 0x00aec160 in ?? () from /usr/lib/kde4/plasma_applet_systemtray.so
#22 0x0626cde0 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#23 0x0626d1e0 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#24 0x00ad42cb in Plasma::Theme::font () from /usr/lib/kde4/plasma_applet_systemtray.so
#25 0x00ad4aa1 in Plasma::Theme::font () from /usr/lib/kde4/plasma_applet_systemtray.so
#26 0x00ae0339 in Plasma::Theme::font () from /usr/lib/kde4/plasma_applet_systemtray.so
#27 0x0626616c in qDeleteInEventHandler () from /usr/lib/libQtCore.so.4                
#28 0x06267b23 in QObject::event () from /usr/lib/libQtCore.so.4
#29 0x0589162c in QApplicationPrivate::notify_helper () from /usr/lib/libQtGui.so.4
#30 0x0589946e in QApplication::notify () from /usr/lib/libQtGui.so.4
#31 0x05365fdd in KApplication::notify () from /usr/lib/libkdeui.so.5
#32 0x062581b1 in QCoreApplication::notifyInternal () from /usr/lib/libQtCore.so.4
#33 0x06258e35 in QCoreApplicationPrivate::sendPostedEvents () from /usr/lib/libQtCore.so.4
#34 0x0625902d in QCoreApplication::sendPostedEvents () from /usr/lib/libQtCore.so.4
#35 0x06282b9f in ?? () from /usr/lib/libQtCore.so.4
#36 0x002e9208 in g_main_context_dispatch () from /lib/libglib-2.0.so.0
#37 0x002ec8b3 in ?? () from /lib/libglib-2.0.so.0
#38 0x002eca71 in g_main_context_iteration () from /lib/libglib-2.0.so.0
#39 0x062827e8 in QEventDispatcherGlib::processEvents () from /usr/lib/libQtCore.so.4
---Type <return> to continue, or q <return> to quit---
#40 0x0592a485 in ?? () from /usr/lib/libQtGui.so.4
#41 0x0625687a in QEventLoop::processEvents () from /usr/lib/libQtCore.so.4
#42 0x06256a3a in QEventLoop::exec () from /usr/lib/libQtCore.so.4
#43 0x062590f5 in QCoreApplication::exec () from /usr/lib/libQtCore.so.4
#44 0x058914a7 in QApplication::exec () from /usr/lib/libQtGui.so.4
#45 0x009f4e46 in kdemain () from /usr/lib/libkdeinit4_plasma.so
#46 0x080486f2 in _start ()

it is a bug in Qt, fixed upstream in Qt.