Let me get this straight. You are using Linux Mint and not Ubuntu 12.04.
The title suggests 12.04 is the problem, but you say it is on Mint 13. Am I
missing something?

They are different beasts. Mint uses a different desktop and window manager
from Ubuntu. There are several versions of Mint 13 as well, Mate, Cinnamon,
and KDE. I cannot picture your screen or problem until I know more.