When changing some settings in Unigine that causes the engine to restart itself (for example shaders quality) after restart the Unigine window disappear. It is still running just there is no window any more. 

4df137691ee29bb812347fa2c5f19095243ede22 is the first bad commit
commit 4df137691ee29bb812347fa2c5f19095243ede22
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Fri May 6 10:31:24 2011 -0700

    GLX/DRI2: handle swap event swap count wrapping
    
    Create a new GLX drawable struct to track client related info, and add a
    wrap counter to it drawable and track it as we receive events.  This
    allows us to support the full 64 bits of the event structure we pass to
    the client even though the server only gives us a 32 bit count.
    
    Reviewed-by: Michel Dänzer <michel@daenzer.net>
    Reviewed-by: Jeremy Huddleston <jeremyhu@apple.com>
    Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

I'm not 100% sure about this commit since the issue is not always reproducible, but it seems likely this can be it.

This is with r300g driver, RV530 card. Assigning to mesa core because of the bisect results, I did try the llvmpipe, to see if other drivers are also affected, however it is so slow here I can't change any settings.

Mesa: 110f846c2578357ebee4e6fab7d71e0e496493d3
GPU: RV530
Kernel: 2.6.40.3-0.fc15.i686 (probably renamed 3.0.3 for some reason)
Xserver: 1.10.3