Comment 7 for bug 751605

A similar problems happens with 12.04, when trying to maximize windows who are larger than the display you want to maximize them on (but will fit on the other display), these windows get maximized on the other display instead. That's pretty counterintuitive to me, windows should just be resized to fit the resolution of the display.

See also this thread: http://askubuntu.com/questions/131177/snap-to-full-screen-not-working-dual-monitors