Version:            (using Devel)
Compiler:          gcc-Version 4.2.4 (Ubuntu 4.2.4-1ubuntu3) 
Installed from:    Compiled sources

Well, from the backtrace this rather looks like a Qt problem than a KWin problem, but since KWin was blamed for the abort...
This crash occured after the upgrade of qt-copy to SVN revision 882016 and applying the latest patches. So it might well be that the problem has been introduced with qt-copy.
KDE SVN revision is 882094.

Application: KWin (kwin), signal SIGABRT
0x00007f1413ff2b50 in nanosleep () from /lib/libc.so.6

Thread 1 (Thread 0x7f14193df730 (LWP 16892)):
[KCrash Handler]
#5  0x00007f1413f87095 in raise () from /lib/libc.so.6
#6  0x00007f1413f88af0 in abort () from /lib/libc.so.6
#7  0x00007f1414cd4a44 in qt_message_output (msgType=QtFatalMsg, buf=0x7fff215d5b70 "ASSERT: \"!receiver->d_func()->postedEvents\" in file kernel/qcoreapplication.cpp, line 1320")
    at global/qglobal.cpp:2102
#8  0x00007f1414cd4b65 in qFatal (msg=0x7f1414e236b8 "ASSERT: \"%s\" in file %s, line %d") at global/qglobal.cpp:2303
#9  0x00007f1414cd4fad in qt_assert (assertion=0x7f1414e64638 "!receiver->d_func()->postedEvents", file=0x7f1414e6419b "kernel/qcoreapplication.cpp", line=1320) at global/qglobal.cpp:1872
#10 0x00007f1414dcdc9b in QCoreApplicationPrivate::removePostedEvents_unlocked (receiver=0x696590, eventType=0, data=0x602370) at kernel/qcoreapplication.cpp:1320
#11 0x00007f1414de4d80 in ~QObject (this=0x696590) at kernel/qobject.cpp:890
#12 0x00007f1415106ad5 in ~QDBusConnectionPrivate (this=0x696590) at qdbusintegrator.cpp:912
#13 0x00007f1415106909 in QDBusConnectionPrivate::deleteYourself (this=0x696590) at qdbusintegrator.cpp:924
#14 0x00007f14150fd02e in ~QDBusConnection (this=0x640c50) at qdbusconnection.cpp:283
#15 0x00007f1415100825 in ~QDBusDefaultConnection (this=0x640c50) at qdbusconnection.cpp:909
#16 0x00007f1415100857 in ~QGlobalStaticDeleter (this=0x7f141535a878) at ../../include/QtCore/../../src/corelib/global/qglobal.h:1557
#17 0x00007f14150fd470 in __tcf_1 () at qdbusconnection.cpp:912
#18 0x00007f1413f8a110 in exit () from /lib/libc.so.6
#19 0x00007f1416bf6a7b in _XDefaultError () from /usr/lib/libX11.so.6
#20 0x00007f1416bf6b6d in _XError () from /usr/lib/libX11.so.6
#21 0x00007f1416bfdc1a in ?? () from /usr/lib/libX11.so.6
#22 0x00007f1416bfdfa5 in _XReply () from /usr/lib/libX11.so.6
#23 0x00007f1416bf28aa in XSync () from /usr/lib/libX11.so.6
#24 0x00007f1416bd28ae in XCloseDisplay () from /usr/lib/libX11.so.6
#25 0x00007f1417dc5bb8 in qt_cleanup () at kernel/qapplication_x11.cpp:2319
#26 0x00007f1417d62798 in ~QApplication (this=0x7fff215dc360) at kernel/qapplication.cpp:1013
#27 0x00007f14177275f5 in ~KApplication (this=0x7fff215dc360) at /home/kde-devel/kde/src/KDE/kdelibs/kdeui/kernel/kapplication.cpp:940
#28 0x00007f141911fc22 in ~Application (this=0x7fff215dc360) at /home/kde-devel/kde/src/KDE/kdebase/workspace/kwin/main.cpp:349
#29 0x00007f1419120fbd in kdemain (argc=3, argv=0x7fff215dc828) at /home/kde-devel/kde/src/KDE/kdebase/workspace/kwin/main.cpp:513
#30 0x00000000004008b3 in main (argc=3, argv=0x7fff215dc828) at /home/kde-devel/kde/build/KDE/kdebase/workspace/kwin/kwin_dummy.cpp:3