Game cannot reliably go fullscreen. When playing, pressing F11 or changing the "Fullscreen" setting in the Video Options sometimes fails to put the game in fullscreen, returning to windowed mode after a short delay. The screen blanks as when going fullscreen successfully, but the windowed mode returns immediately.

Only happens when an actual game is running. Doesn't happen at the title screen, happens when the in-game menu is accessed (via ESC).

It often takes 5-10 switches (either through options or F11) to get to fullscreen. Opening menus, defocusing and refocusing the game window and other voodoo might help, but not reliably.

Possibly related: Sometimes when the fullscreen mode is entered, the player is unable to turn around more than a fixed amount (as if the cursor was confined to the earlier, small window or went outside and did not register).