I cannot recreate it intentionally, although I have tried. It starts about 5 mins into the round. It seems to happen during heavy fire and when I'm pressing numerous buttons (forward, straf, jump, left click) at the same time. It's not just a beep, the controls lock up. So if i was firing, then even if i let go of the mouse, i still fire in-game. Or if i was straffing left, after the beep, I will not touch the keyboard but the charector is still straffing left. I checked the atari forums, and there is no instance of this that I could find, which is why I'm wondering if it is a problem with the laptop itself.
Yes this is the demo.