Comment 8 for bug 1425701

Good point. Well, compiz was my best guess to make a bug report, as
- I was experiencing the same issue with gnome classic (Compiz) but not with Metacity, nor gnome3.
- The errors in unity log didn't look nice... Disabling framebuffer option in opelgl plugin improved the situation a little (does it for you?)
- When I downgraded compiz, there were a few packages with "compiz" on their name, but I didn't actually downgraded all of them as some tried to unninstall unity when I selected the old version.
- Using nouveau, Unity worked fine for me (apart from other issues I have with nouveau that make it unusable, but are unrelated to this)

BTW I used
   unity --replace --log=unity.log
in tty1 to save all unity output, maybe you can get some clues that way