I've updated my 13.1 after a while again and now I have some really nasty graphical glitches. It seems like there is something going on in the double buffering of widgets, resulting on old content "flickering" in for a while. The problem is worst in Firefox, but I also see it in other applications and Gnome itself. I have not really found anything, except I saw a bug report like that for Firefox. But then again it does not only affect Firefox for me.