This happens to me when I use the Internet Explorer. My best guess is, that the problem is, that the game tries to use all the computing power available. The game does use the "setTimeout(Loop, 0)" trick to accomplish this. Usually there is no problem if the event queue is a queue. Then the setTimeout function is the last one in the queue and keypresses are handled first. If the events are handled differently, for example by using a stack, such games are in big trouble.