Hello guys.
I've been playing the build engine games recently using my preferred control setup of using WSAD to move and the arrows to aim. For some reason, every so often, my game will stop registering aiming and strafe instead (as if the ALT key is pushed down), and only ALT-TABing out of the game, or ENTER+ALTing to change out of fullscreen, fix it, until it undoubtably happens again. Does anyone have any idea why this issue occurs, or how to fix it?

Thanks in advance.

I may have found a fix. I have switched my controls from Keyboard + Mouse to just Keyboard. Only time will tell if it truly fixed it.

Considering pretty much all Build engine games sold on GOG run using DOSBox, you could also try the DOSBox Mapper (Ctrl+F1) to rebind the keys. This is especially useful for those games that have no in-game way of rebinding controls, such as a (not Build engine) "vanilla" Realms of the Haunting.