Hi friends, I have this bug too. I've reinstalled the whole system and the problem remains. I have an Intel Sandybridge Mobile i5-2410M. All up-to-date, with 'wheezy' on the sources.list
This bug is really disturbing, I've installed Trisquel on a virtual machine just to use LibreOffice. This bug is annoying me for about a year. Sometimes, when the system freezes and I stop touch computer for about 15 seconds, the screen goes black and came back from hell, as if nothing happened. But this is rare. Almost every time, reboot is needed. Regards.
