I have also been observing such corruption since quite some time on a GM965 with KMS+DRI2. I think this issue is similar (if not the same) to that reported in the upstream bug fd.o #21415.
regards, Stefano -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org