Description of problem:
X sometimes crashes when I hit Alt-Tab.

Version-Release number of selected component (if applicable):
X.Org X Server 1.9.5

How reproducible:
Intermittent -- can't reproduce on demand.

Steps to Reproduce:
1.  Type Alt-Tab
2.
3.
  
Actual results:
Crash

Expected results:
Display windows to switch to

Additional info:
KDE 4.6.3-1 Desktop effects enabled

Stack Trace:

(gdb) bt
#0  0x0000003ec20330c5 in raise (sig=6)
    at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
#1  0x0000003ec2034a76 in abort () at abort.c:92
#2  0x000000000046380e in OsAbort () at utils.c:1288
#3  0x000000000046f1d7 in ddxGiveUp () at xf86Init.c:951
#4  0x000000000045fc7d in AbortServer () at log.c:424
#5  0x000000000045fe8e in FatalError (
    f=0x579870 "Caught signal %d (%s). Server aborting\n") at log.c:552
#6  0x0000000000460eee in OsSigHandler (signo=11, sip=<value optimized out>, 
    unused=<value optimized out>) at osinit.c:156
#7  <signal handler called>
#8  0x00007ff329de35c8 in DrawableGone (glxPriv=0x1b01a30, xid=24037264)
    at glxext.c:133
#9  0x000000000044a2ee in FreeResource (id=24037264, skipDeleteFuncType=0)
    at resource.c:601
#10 0x0000000000428db6 in ProcFreePixmap (client=0xfcde40) at dispatch.c:1448
#11 0x000000000042d521 in Dispatch () at dispatch.c:432
#12 0x000000000042157e in main (argc=8, argv=<value optimized out>, 
    envp=<value optimized out>) at main.c:291
(gdb)