When the graphical boot sequence has completed, but before the gdm login screen appears, the X server seems to restart. And when it does, the screen is dirty like zebra...
Created attachment 419135 [details]
Can you attach your X log please?
I presume that the garbled screen disappears and X runs fine afterwards?
Created attachment 419252 [details]
Yes, X runs fine afterwards. The garbled screen lasts only a few seconds. Not really much of a problem, but it does make a bit of a mockery of the pretty graphical boot sequence.
Yup, I know. I was just asking to make sure it wasn't a more serious bug than I was suspecting :) This issue is known already, it occurs only in multiple display configurations.
*** This bug has been marked as a duplicate of bug 582489 ***