Hi,
Is it worth filing a report of this on bugzilla? It is not something I
can reproduce at will; it just seems to kinda happen.
This is not a problem with compiz, but the nvidia driver. So no point
filling a bug against compiz ;)
See
http://www.nvnews.net/vbulletin/showthread.php?t=100803
bottom line - nvidia cliams the bug will be fixed in the next driver
release. In the meantime nothing you can do other than restart every now
and then (I have the same issue, and just logout and in again now and then).
Chris