BZFlag - Multiplayer 3D Tank Game

Thanks for the info. It's quite unexpected to tie the window resizability
to "confine mouse". Also, one would think that the window would retain the
aspect ratio of the full-screen mode that the user selected.

I wouldn't exactly classify this as a bug as the window is simply and
intentionally created at a fixed size that should work on most all systems.
Once windowed, you can resize the window to your desired ratio and you can
start BZFlag directly to a window with your exact desired ratio as well
(see -geometry and -window options).

Screen shot attached, comparing windowed and full-screen modes.