In Compiz, re-redirecting an unredirected OpenGL window sometimes kills the X server.

Test case:
  1. Enable "Unredirect Fullscreen Windows" in CCSM > Composite.
  2. Start an OpenGL game, or video with: mplayer -vo gl ...
  3. Trigger scale (Shift+Alt+Up) or the window menu (Alt+Space)
If it doesn't crash, then repeat.

Expected: Either windows scale or the window menu appears
Observed: Sometimes, just sometimes, X crashes and I get sent back to the login screen.

Program received signal SIGSEGV, Segmentation fault.
0x00007f12ea7f1e24 in drm_intel_bo_is_reusable ()
   from /usr/lib/x86_64-linux-gnu/libdrm_intel.so.1
(gdb) bt
#0 0x00007f12ea7f1e24 in drm_intel_bo_is_reusable ()
   from /usr/lib/x86_64-linux-gnu/libdrm_intel.so.1
#1 0x00007f12eaa1ecfb in intel_set_pixmap_bo (pixmap=0x7f12efcf2370, bo=0x0)
    at ../../src/intel_uxa.c:643
#2 0x00007f12eaa1eec7 in intel_uxa_destroy_pixmap (pixmap=0x7f12efcf2370)
    at ../../src/intel_uxa.c:1108
#3 0x00007f12ee763f60 in damageDestroyPixmap (pPixmap=0x7f12efcf2370)
    at ../../../miext/damage/damage.c:1652
#4 0x00007f12eb692402 in XvDestroyPixmap (pPix=0x7f12efcf2370)
    at ../../Xext/xvmain.c:387
#5 0x00007f12ee73980a in ShmDestroyPixmap (pPixmap=0x7f12efcf2370)
    at ../../Xext/shm.c:276
#6 0x00007f12eaa3070b in I830DRI2DestroyBuffer (drawable=<optimised out>,
    buffer=<optimised out>) at ../../src/intel_dri.c:434
#7 0x00007f12eac5e97b in DRI2DrawableGone (p=0x7f12ef829d20,
    id=<optimised out>) at ../../../../hw/xfree86/dri2/dri2.c:309
#8 0x00007f12ee6be5c2 in doFreeResource (res=0x7f12ef829db0, skip=0)
    at ../../dix/resource.c:571
#9 0x00007f12ee6bf2fa in FreeClientResources (client=0x7f12efa19d80)
    at ../../dix/resource.c:853
#10 0x00007f12ee69cd2a in CloseDownClient (client=0x7f12efa19d80)
    at ../../dix/dispatch.c:3477
#11 0x00007f12ee69d8b6 in Dispatch () at ../../dix/dispatch.c:454
#12 0x00007f12ee68c7ba in main (argc=8, argv=<optimised out>,
    envp=<optimised out>) at ../../dix/main.c:287
(gdb)

With:
libdrm-intel1                          2.4.32-1ubuntu1
xserver-xorg-video-intel               2:2.17.0-1ubuntu4.1
xserver-xorg                           1:7.6+12ubuntu1