Comment 9 for bug 751605

This happens in Precise too, but I think it's not only related to having monitors with different resolutions, in fact sometimes the window is correctly maximized to the smaller monitor.

The bug is triggered when you try to maximize a window that is taller or larger than the monitor you're trying to maximize the window to, such when you drag a maximized window from a bigger monitor to the smaller and the automatically restored unmaximized window size is bigger on one of the two dimensions in respect to the monitor you're dragging the window to.

Seems there's a simple flaw in the governing logic, hope will be fixed soon and the patch backported to Precise.