My key did this also, the thing is after a while the key wouldnt switch the imobiliser off when i was in the car so had to have a whole new key and it had to be programed, its best to ask the stealers before it gets to that stage as they might just reprogram the key for you.
i'll ask it later when I get back to it see if it works, come 2 think of it I was quite nasty, I did say "open u t**t" - maybe it does not like been abused haha