https://bugs.freedesktop.org/show_bug.cgi?id=57567
--- Comment #10 from Vladimir bobahu4@gmail.com --- Some news which makes it easier to isolate the bug
ubuntu updated kernel to 3.5.0-22 and bug appeared on this kernel 3.5.0-21 - no bug
looks like they added some upstream changes.
here is list of changes 21 to 22 from their deb pkg for kernel - http://pastebin.com/4uUWUtLV