Comment 19 for bug 321224

other thoughts:
1) after startup (with the screen shifted), if I put the system on sleep and then wake it up the screen is ok

2) like someone else noted, I also verified that if I run glxgears from terminal and than terminate it with CTRL+C the screen shifts to the right (only once, so doing it more times doesn't change anything, the shift about 20pixels absolute, and not relative to the previous position). anyway terminating glxgears simply closing its window does not shift the screen, but gives this output on the terminal:
XIO: fatal IO error 11 (Resource temporarily unavailable) on X server ":0.0"
         after 42 requests (42 known processed) with 0 events remaining.

3) after startup (screen shifted) I can adjust it switching to another tty console and back (CTRL+ALT+F1 -> CTRL+ALT+F7)