Ubuntu
xserver-xorg-video-nouveau package

  1. Bug #921540
  2. Comment #3

Comment 3 for bug 921540

Revision history for this message
Bryce Harrington (bryce) wrote : Re: Multimonitor setup breaks and reverts to mirror setup randomly and while watching youtube videos

Typically behavior such as you describe is due to gnome-settings-daemon crashing.

The issues you describe in comment #2 sound like Unity issues and should be reported separately.