Car locked with engine running.

Hi. I was wondering if anybody on here knows why this happened or had a similar problem themselves:

I was leaving work in Ilford at 1am this morning. I started the engine and set all the heaters and fans on high to warm the car and clear the windscreen.

I got out to use the ice-scraper on the front windscreen but when I went to get back in the car the door wouldn't open, in fact none of them would.

I'm now locked outside the car in sub-zero temperatures with the engine running.

Fortunately my partner was awake and came out from Chelmsford with the spare key so I could manually unlock the car (the little plastic stick key thing was in my bag, locked inside the car).

Curiously the red flashing LED on the door wasn't illuminated to say the car had locked and enabled the alarm/immobiliser.

The car is an Audi A4 Avant Special Edition (2008). High miles at 152,000. I've had the car from new and never had this before.

Is this:

A. Something I did wrong?

B. A fluke accident?

C. A known problem with this model?

D. A possible wiring problem?

Any ideas, hints, tips or suggestions welcome before I take the car back to Audi (again). (Had a few problems recently, I'm guessing due to mileage, but quite frankly the car has turned into John Carpenter's Christine (from the '80s film) and I'm seriously getting annoyed now, hate driving her as I don't trust her.)