I got this problem a lot when I played on windowed mode. I usually only noticed
it because I couldn't click on 'scroll down' button on the dialog mode.
This error was present on 0.14 and if I'm not mistaken on 0.15 as well. I use
gnome, but my other netbook runs unity. They all are ubuntu 12.04.
Strangely, after using git version I didn't saw anymore this bug. Not that I
could get they to often, the massive dialogs which used to force me to try to
press that button are long gone.