I don't think it's a key sticking, but I have no explanation. I agree it seems to happen at the worst times. But when it happens, try alt-tabbing out of the game (like to a web page or your desktop) then go back to the game. That's what fixes it for me. I totally understand what you're talking about. I assume it's something on my end but it's random, I couldn't duplicate it, and luckily pretty rare, and at least easily dealt with.