Version:           Unbekannt (using 4.2.3 (KDE 4.2.3) "release 116", KDE:KDE4:Factory:Desktop / openSUSE_11.1)
Compiler:          gcc
OS:                Linux (i686) release 2.6.27.21-0.1-default

I was using Alt-Tab to switched windows with compositing. I am using the "Kasten mit Minibildern"-Effect (Guessing form the backtrace this is the box switch effect).

I could not reproduce this so far.

Backtrace:

Anwendung: KWin (kwin), Signal SIGSEGV
[?1034h[Thread debugging using libthread_db enabled]
[Current thread is 1 (Thread 0xb64c5700 (LWP 3338))]

Thread 1 (Thread 0xb64c5700 (LWP 3338)):
[KCrash Handler]
#6  0x080de0e5 in ?? ()
#7  0xb43732dc in KWin::BoxSwitchEffect::paintWindowThumbnail (this=0x8500728, w=0x83fa368) at /usr/src/debug/kdebase-workspace-4.2.3/kwin/effects/boxswitch.cpp:761
#8  0xb43765b2 in KWin::BoxSwitchEffect::paintScreen (this=0x8500728, mask=0, region={d = 0xbfde4208, static shared_empty = {ref = {_q_value = 461}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, 
    data=@0xbfde42d8) at /usr/src/debug/kdebase-workspace-4.2.3/kwin/effects/boxswitch.cpp:147
#9  0xb8084d9f in KWin::EffectsHandlerImpl::paintScreen (this=0x8370420, mask=0, region={d = 0xbfde4258, static shared_empty = {ref = {_q_value = 461}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, 
    data=@0xbfde42d8) at /usr/src/debug/kdebase-workspace-4.2.3/kwin/effects.cpp:122
#10 0xb43d0680 in KWin::TrackMouseEffect::paintScreen (this=0x8450cf8, mask=0, region={d = 0xbfde4298, static shared_empty = {ref = {_q_value = 461}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, 
    data=@0xbfde42d8) at /usr/src/debug/kdebase-workspace-4.2.3/kwin/effects/trackmouse.cpp:71
#11 0xb8084d9f in KWin::EffectsHandlerImpl::paintScreen (this=0x8370420, mask=0, region={d = 0xbfde4330, static shared_empty = {ref = {_q_value = 461}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, 
    data=@0xbfde42d8) at /usr/src/debug/kdebase-workspace-4.2.3/kwin/effects.cpp:122
#12 0xb8072350 in KWin::Scene::paintScreen (this=0x83f5338, mask=0xbfde43b4, region=0xbfde4474) at /usr/src/debug/kdebase-workspace-4.2.3/kwin/scene.cpp:133
#13 0xb807ecea in KWin::SceneOpenGL::paint (this=0x83f5338, damage={d = 0xbfde4474, static shared_empty = {ref = {_q_value = 461}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, toplevels=
        {{p = {static shared_null = {ref = {_q_value = 5900}, alloc = 0, begin = 0, end = 0, sharable = 1, array = {0x0}}, d = 0xbfde4470}, d = 0xbfde4470}})
    at /usr/src/debug/kdebase-workspace-4.2.3/kwin/scene_opengl.cpp:724
#14 0xb806dca6 in KWin::Workspace::performCompositing (this=0x80d1730) at /usr/src/debug/kdebase-workspace-4.2.3/kwin/composite.cpp:384
#15 0xb800e53d in KWin::Workspace::qt_metacall (this=0x80d1730, _c=QMetaObject::InvokeMetaMethod, _id=140, _a=0xbfde4548) at /usr/src/debug/kdebase-workspace-4.2.3/build/kwin/workspace.moc:445
#16 0xb6f1f580 in QMetaObject::activate (sender=0x80d1984, from_signal_index=4, to_signal_index=4, argv=0x0) at kernel/qobject.cpp:3031
#17 0xb6f20302 in QMetaObject::activate (sender=0x80d1984, m=0xb6ff2904, local_signal_index=0, argv=0x0) at kernel/qobject.cpp:3101
#18 0xb6f5a7f7 in QTimer::timeout (this=0x80d1984) at .moc/release-shared/moc_qtimer.cpp:126
#19 0xb6f25f9e in QTimer::timerEvent (this=0x80d1984, e=0xbfde4a20) at kernel/qtimer.cpp:257
#20 0xb6f1a04f in QObject::event (this=0x80d1984, e=0xbfde4a20) at kernel/qobject.cpp:1120
#21 0xb71798fc in QApplicationPrivate::notify_helper (this=0x8057ad8, receiver=0x80d1984, e=0xbfde4a20) at kernel/qapplication.cpp:3803
#22 0xb718175e in QApplication::notify (this=0xbfde4d24, receiver=0x80d1984, e=0xbfde4a20) at kernel/qapplication.cpp:3393
#23 0xb7dc20cd in KApplication::notify (this=0xbfde4d24, receiver=0x80d1984, event=0xbfde4a20) at /usr/src/debug/kdelibs-4.2.3/kdeui/kernel/kapplication.cpp:307
#24 0xb8022fed in KWin::Application::notify (this=0xbfde4d24, o=0x80d1984, e=0xbfde4a20) at /usr/src/debug/kdebase-workspace-4.2.3/kwin/main.cpp:368
#25 0xb6f0a961 in QCoreApplication::notifyInternal (this=0xbfde4d24, receiver=0x80d1984, event=0xbfde4a20) at kernel/qcoreapplication.cpp:587
#26 0xb6f38b86 in QTimerInfoList::activateTimers (this=0x805aacc) at kernel/qcoreapplication.h:209
#27 0xb6f35060 in timerSourceDispatch (source=0x805aa98) at kernel/qeventdispatcher_glib.cpp:160
#28 0xb65d79c8 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#29 0xb65db083 in ?? () from /usr/lib/libglib-2.0.so.0
#30 0xb65db241 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#31 0xb6f34fb8 in QEventDispatcherGlib::processEvents (this=0x8057c28, flags={i = -1075950648}) at kernel/qeventdispatcher_glib.cpp:319
#32 0xb72127c5 in QGuiEventDispatcherGlib::processEvents (this=0x8057c28, flags={i = -1075950600}) at kernel/qguieventdispatcher_glib.cpp:198
#33 0xb6f0901a in QEventLoop::processEvents (this=0xbfde4c70, flags={i = -1075950536}) at kernel/qeventloop.cpp:143
#34 0xb6f091da in QEventLoop::exec (this=0xbfde4c70, flags={i = -1075950472}) at kernel/qeventloop.cpp:194
#35 0xb6f0b895 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:845
#36 0xb7179777 in QApplication::exec () at kernel/qapplication.cpp:3331
#37 0xb802603a in kdemain (argc=3, argv=0xbfde4ef4) at /usr/src/debug/kdebase-workspace-4.2.3/kwin/main.cpp:519
#38 0x080487b2 in main (argc=-1271000088, argv=0xb6a48201) at /usr/src/debug/kdebase-workspace-4.2.3/build/kwin/kwin_dummy.cpp:3