This sounds like the known synchronization problems between GLX and Damage that are inherent in the design of those extensions. See this thread for a discussion of the currently proposed fix:
http://lists.x.org/archives/xorg-dev...st/011830.html
http://lists.x.org/archives/xorg-dev...st/011835.html
Short version: Compiz can handle Damage events in response to rendering before the rendering has actually occurred.