Comment 5 for bug 927248

One other thing I might add, I noticed Mesa 8.0 is in Precise. There has been a lot of talk on Phronix and other blogs about Mesa 8.0 and the llvmpipe driver which can be used for software rendering on non-accelerated HW. Fedora 17 plans on using llvmpipe to allow gnome-shell on non-accelerated HW. When was Mesa 8.0 pushed? A bug or issue with Mesa 8.0 might be able to explain this bug.

1) It would explain why Unity doesn't autofailback to Unity 2D (It takes the llvmpipe driver as sufficient).
2) If there are issues with Mesa it would explain the corrupted screens and why Unity 2D functions properly.