http://bugs.winehq.org/show_bug.cgi?id=30341
--- Comment #6 from Ralf Jung ralfjung-e@gmx.de 2012-04-04 05:43:28 CDT --- (In reply to comment #5)
The size of a maximized window is set to the screen size minus the caption. That's how Windows does it. Ideally it would be adjusted based on the wm metrics, but that's pretty hard to do, and it's not clear that apps would be able to cope with a window larger than the screen.
15 pixels is not even the size of a title bar here - title bars have a height of 20 pixels (if they are shown). And still it used to work before. Also, this is not Wine maximizing a window - the maximization is done by the window manager.