Update: the problem seems to go away if you turn gnome-screensaver off. So this might be related to bug <a href="https://bugs.launchpad.net/ubuntu/+source/compiz/+bug/144663">Bug #144663</a> (the Xorg.0.log.old seem the same), although I did experience the problem without compiz running.
Update: the problem seems to go away if you turn gnome-screensaver off. So this might be related to bug <a href="https:/ /bugs.launchpad .net/ubuntu/ +source/ compiz/ +bug/144663">Bug #144663</a> (the Xorg.0.log.old seem the same), although I did experience the problem without compiz running.