Key.isDown issues... three-key combos

I’m working on a game where movement is controlled with WASD, and other commands are controlled with YUIOHJKLNM<>. The problem I’m encountering occurs when pressing down certain combinations of three keys. For example, when I’m holding down J and M, the ASD keys won’t work; only W will. The same applies to J and N, and K and <; W is the only key of the movement commands that will work.

There is nothing in my programming that I can see or find that is causing this error; I’ve performed several tests and managed to pretty much isolate the problem being something to do with the keycodes. Does actionscript 2.0 have some inherent issues with certain 3-key combinations being pressed?