Application: kwin (4.11.21)
KDE Platform Version: 4.14.10 (Compiled from sources)
Qt Version: 4.8.7
Operating System: Linux 3.16.7-7-desktop x86_64
Distribution: "openSUSE 13.2 (Harlequin) (x86_64)"

-- Information about the crash:
- What I was doing when the application crashed: 

Since kwin_x11 crashes for me (separate report coming), I'm using kwin from KDE4, while plasma is from plasma5. If you don't care for this strange mix, feel free to close this bug :-)

Somehow I was able to see Plasma (the shell) in the Alt-Tab list.
When I alt-tab'ed to it, kwin crashed.

After kwin's autorestart, Plasma is no longer in the Alt-Tab list.

-- Backtrace:
Application: KWin (kwin), signal: Segmentation fault
Using host libthread_db library "/lib64/libthread_db.so.1".
[KCrash Handler]
#6  0x0000000001bf2000 in  ()
#7  0x00007fade385515d in KWin::Workspace::constrainedStackingOrder() (this=this@entry=0x1723ca0) at /d/kde/src/4/kde/kde-workspace/kwin/layers.cpp:509
#8  0x00007fade3855730 in KWin::Workspace::updateStackingOrder(bool) (this=this@entry=0x1723ca0, propagate_new_clients=<optimized out>) at /d/kde/src/4/kde/kde-workspace/kwin/layers.cpp:117
#9  0x00007fade3855acd in KWin::Workspace::blockStackingUpdates(bool) (propagate_new_clients=<optimized out>, this=0x1723ca0) at /d/kde/src/4/kde/kde-workspace/kwin/layers.cpp:609
#10 0x00007fade3855acd in KWin::Workspace::blockStackingUpdates(bool) (this=this@entry=0x1723ca0, block=block@entry=false) at /d/kde/src/4/kde/kde-workspace/kwin/layers.cpp:616
#11 0x00007fade3845504 in KWin::Client::releaseWindow(bool) (this=<synthetic pointer>, __in_chrg=<optimized out>) at /d/kde/src/4/kde/kde-workspace/kwin/workspace.h:565
#12 0x00007fade3845504 in KWin::Client::releaseWindow(bool) (this=this@entry=0x1e77150, on_shutdown=on_shutdown@entry=false) at /d/kde/src/4/kde/kde-workspace/kwin/client.cpp:317
#13 0x00007fade3860daa in KWin::Client::unmapNotifyEvent(XUnmapEvent*) (this=0x1e77150, e=<optimized out>) at /d/kde/src/4/kde/kde-workspace/kwin/events.cpp:595
#14 0x00007fade3862e7b in KWin::Client::windowEvent(_XEvent*) (this=0x1e77150, e=e@entry=0x7fffaf7d8610) at /d/kde/src/4/kde/kde-workspace/kwin/events.cpp:451
#15 0x00007fade38644bf in KWin::Workspace::workspaceEvent(_XEvent*) (this=0x1723ca0, e=e@entry=0x7fffaf7d8610) at /d/kde/src/4/kde/kde-workspace/kwin/events.cpp:164
#16 0x00007fade38588b0 in KWin::Application::x11EventFilter(_XEvent*) (this=0x7fffaf7d89c0, e=0x7fffaf7d8610) at /d/kde/src/4/kde/kde-workspace/kwin/main.cpp:422
#17 0x00007faddc10d2e5 in qt_x11EventFilter(XEvent*) (ev=0x7fffaf7d8610) at kernel/qapplication_x11.cpp:436
#18 0x00007faddc11cbd2 in QApplication::x11ProcessEvent(_XEvent*) (this=0x7fffaf7d89c0, event=0x7fffaf7d8610) at kernel/qapplication_x11.cpp:3354
#19 0x00007faddc158853 in QEventDispatcherX11::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x14a81d0, flags=...) at kernel/qeventdispatcher_x11.cpp:132
#20 0x00007faddd240512 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x7fffaf7d8820, flags=...) at kernel/qeventloop.cpp:149
#21 0x00007faddd24069c in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x7fffaf7d8820, flags=...) at kernel/qeventloop.cpp:204
#22 0x00007faddd24386e in QCoreApplication::exec() () at kernel/qcoreapplication.cpp:1227
#23 0x00007faddc07ac2e in QApplication::exec() () at kernel/qapplication.cpp:3823
#24 0x00007fade3859763 in kdemain(int, char**) (argc=3, argv=0x7fffaf7d8b08) at /d/kde/src/4/kde/kde-workspace/kwin/main.cpp:597
#25 0x00007faddaab4b05 in __libc_start_main (main=0x400a60 <main(int, char**)>, argc=3, argv=0x7fffaf7d8b08, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fffaf7d8af8) at libc-start.c:285
#26 0x0000000000400a8e in _start () at ../sysdeps/x86_64/start.S:122

Reported using DrKonqi