Version:            (using Devel)
Installed from:    Compiled sources
OS:                Linux

Here is the backtrace

Application: KWin (kwin), signal SIGABRT
Using host libthread_db library "/lib/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread 0x7f1c23d98740 (LWP 30074)]
[KCrash handler]
#5  0x00007f1c1e4dc3a5 in *__GI_raise (sig=<value optimized out>)
    at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
#6  0x00007f1c1e4dd71e in *__GI_abort () at abort.c:88
#7  0x00007f1c1e4d5aff in *__GI___assert_fail (
    assertion=0x7f1c1e3ab9bb "!c->xlib.lock", 
    file=0x7f1c1e3ab9b0 "xcb_xlib.c", line=41, 
    function=0x7f1c1e3aba10 "xcb_xlib_lock") at assert.c:78
#8  0x00007f1c1e3ab95a in xcb_xlib_lock () from /usr/lib/libxcb-xlib.so.0
#9  0x00007f1c23351ef2 in _XCBLockDisplay (dpy=0x61e440) at xcb_lock.c:21
#10 0x00007f1c22bd4574 in XRenderFreePicture () from /usr/lib/libXrender.so.1
#11 0x00007f1c2077a0cf in QX11PixmapData::release (this=0x7b9200)
    at image/qpixmap_x11.cpp:1162
#12 0x00007f1c2077a3e0 in ~QX11PixmapData (this=0x757a)
    at image/qpixmap_x11.cpp:1141
#13 0x00007f1c2077279d in QPixmap::deref (this=0x8c1df0)
    at image/qpixmap.cpp:1260
#14 0x00007f1c207727c8 in ~QPixmap (this=0x757a) at image/qpixmap.cpp:321
#15 0x00007f1c192f70b8 in QCache<unsigned long long, QPixmap>::clear (
    this=0x8a90e8) at /usr/include/qt4/QtCore/qcache.h:140
#16 0x00007f1c192f70ed in ~QCache (this=0x757a)
    at /usr/include/qt4/QtCore/qcache.h:104
#17 0x00007f1c192f7115 in ~OxygenHelper (this=0x8a9090)
    at /var/tmp/portage/kde-base/kdebase-9999.4/work/kdebase-9999.4/workspace/kwin/clients/ozone/lib/helper.h:39
#18 0x00007f1c1e4de9c9 in *__GI_exit (status=1) at exit.c:75
#19 0x00007f1c2334bb71 in _XDefaultError (dpy=0x61e440, event=0x7fff2bef7760)
    at XlibInt.c:2853
#20 0x00007f1c2334bc30 in _XError (dpy=0x61e440, rep=0x89b770)
    at XlibInt.c:2905
#21 0x00007f1c233526d5 in process_responses (dpy=0x61e440, 
    wait_for_first_event=0, current_error=0x7fff2bef78a8, 
    current_request=152780) at xcb_io.c:138
#22 0x00007f1c23352a20 in _XReply (dpy=0x61e440, rep=0x7fff2bef78f0, extra=0, 
    discard=1) at xcb_io.c:370
#23 0x00007f1c23347de6 in XSync (dpy=0x61e440, discard=1) at Sync.c:48
#24 0x00007f1c2332a7e2 in XCloseDisplay (dpy=0x61e440) at ClDisplay.c:67
#25 0x00007f1c20720fe8 in qt_cleanup () at kernel/qapplication_x11.cpp:2325
#26 0x00007f1c206caf63 in ~QApplication (this=0x7fff2bef7ad0)
    at kernel/qapplication.cpp:1020
#27 0x00007f1c23a67c46 in kdemain (argc=3, argv=0x7fff2bef7f88)
    at /var/tmp/portage/kde-base/kdebase-9999.4/work/kdebase-9999.4/workspace/kwin/main.cpp:511
#28 0x00007f1c1e4c9b54 in __libc_start_main (main=0x400940 <main>, argc=3, 
    ubp_av=0x7fff2bef7f88, init=<value optimized out>, 
    fini=<value optimized out>, rtld_fini=<value optimized out>, 
    stack_end=0x7fff2bef7f78) at libc-start.c:229
#29 0x00000000004008c9 in _start ()
#0  0x00007f1c1e53e790 in __nanosleep_nocancel () from /lib64/libc.so.6