Auto-locking Focus

[jmc41]

Strange one here, I opened up the car and turned it on, grabbed de-icer and scrapper and closed door.
Ignoring the whole enviromental issue with doing this for 2 minutes please I sprayed the car down, opened passenger door and chucked de-icer in, closed door.
The Car locked. With my Keys inside - car keys, house keys, everything.

Fortunately I was a) at home and b) quickly worked out that if I banged on the door someone could let me in and I'd grab the spare key. But what the heck happened? If I'd been at work the only solution that springs to mind is smashing the window in... Or going home, picking up spare key and coming back even assuming someone is at home - plus the car was running with a fairly full tank of petrol.

I'm going to have to use the spare key I think and keep the locking/unlocking fob and house keys on my trousers during the winter but thats a real pain.