https://bugs.freedesktop.org/show_bug.cgi?id=32688
--- Comment #2 from Marek Olšák maraeo@gmail.com 2011-01-23 15:58:25 PST --- This bug is r500-only as far as I can tell.
I have just found a way to trigger it very easily: enable offset mapping in nexuiz. If you disable it, the problem will go away. Given this fact, I believe it's a bug in our r500 fragment shader backend.