I don't know... I haven't tried Windows 8.1 yet.
Have you tried setting the program for "compatibiility mode"?
In the thread about mouse problems with Windows 8.1 (
http://openarena.ws/board/index.php?topic=4853.0), Aozora linked a different version of SDL.dll file, that solved a
side problem caused by the workaround for mouse problem. Maybe you may even try that dll, although I don't know if that may help with your problem or not.