Version:           4.5 (using KDE 4.5.0) 
OS:                Linux

Fairly simple:
Press Ctrl + F8 (shortcut for desktop grid) and keep it pressed. You can see the grid and desktop changing very fast, and after 1-2 seconds KWin crashes. Short before it crashes you can see a part of the desktop grid effect over your current open application.
I know that this isn't the typical behaviour of a user that wants to use the effect, but it's ugly if that happens.

A (hopefully simple) solution would be if a timer controls the animation and allows to enable/disable desktop grid first after the animation has ended.



Here's the crash info (maybe not useful, because i don't use debug flags):

Application: KWin (kwin), signal: Segmentation fault
Traceback (most recent call last):
  File "/usr/share/gdb/auto-load/usr/lib64/gcc/x86_64-pc-linux-gnu/4.5.1/libstdc++.so.6.0.14-gdb.py", line 59, in <module>
    from libstdcxx.v6.printers import register_libstdcxx_printers
ImportError: No module named libstdcxx.v6.printers
[KCrash Handler]
#5  0x00007f0763be277a in ?? () from /usr/lib64/kde4/kwin4_effect_builtins.so
#6  0x00007f0763be3622 in ?? () from /usr/lib64/kde4/kwin4_effect_builtins.so
#7  0x00007f07796a4597 in ?? () from /usr/lib/libkdeinit4_kwin.so
#8  0x00007f07796a4597 in ?? () from /usr/lib/libkdeinit4_kwin.so
#9  0x00007f07796a4597 in ?? () from /usr/lib/libkdeinit4_kwin.so
#10 0x00007f07796a4597 in ?? () from /usr/lib/libkdeinit4_kwin.so
#11 0x00007f07796a4597 in ?? () from /usr/lib/libkdeinit4_kwin.so
#12 0x00007f07796a4597 in ?? () from /usr/lib/libkdeinit4_kwin.so
#13 0x00007f07796a4597 in ?? () from /usr/lib/libkdeinit4_kwin.so
#14 0x00007f0779688e9e in ?? () from /usr/lib/libkdeinit4_kwin.so
#15 0x00007f077969c8a2 in ?? () from /usr/lib/libkdeinit4_kwin.so
#16 0x00007f0779680c71 in ?? () from /usr/lib/libkdeinit4_kwin.so
#17 0x00007f07795f169f in ?? () from /usr/lib/libkdeinit4_kwin.so
#18 0x00007f0774f08d57 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib64/qt4/libQtCore.so.4
#19 0x00007f0774f0b859 in QObject::event(QEvent*) () from /usr/lib64/qt4/libQtCore.so.4
#20 0x00007f0775b537d4 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib64/qt4/libQtGui.so.4
#21 0x00007f0775b5a13f in QApplication::notify(QObject*, QEvent*) () from /usr/lib64/qt4/libQtGui.so.4
#22 0x00007f0778df3fb6 in KApplication::notify(QObject*, QEvent*) () from /usr/lib/libkdeui.so.5
#23 0x00007f0774ef16db in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib64/qt4/libQtCore.so.4
#24 0x00007f0774f23476 in ?? () from /usr/lib64/qt4/libQtCore.so.4
#25 0x00007f0774f24640 in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/qt4/libQtCore.so.4
#26 0x00007f0775bfaf27 in ?? () from /usr/lib64/qt4/libQtGui.so.4
#27 0x00007f0774ef01a2 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/qt4/libQtCore.so.4
#28 0x00007f0774ef03e4 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/qt4/libQtCore.so.4
#29 0x00007f0774ef50bb in QCoreApplication::exec() () from /usr/lib64/qt4/libQtCore.so.4
#30 0x00007f0779616643 in kdemain () from /usr/lib/libkdeinit4_kwin.so
#31 0x00007f077924fcdd in __libc_start_main () from /lib/libc.so.6
#32 0x0000000000400789 in _start ()

Reproducible: Always

Steps to Reproduce:
Press Ctrl + F8 and keep it pressed!

Actual Results:  
KWin crash report and KWin restarts.

Expected Results:  
Show the animation as long as i press the keys ;)