Opel Vectra Windows Opening!

I have a 1.9L CDTI (150bhp) '07 Opel Vectra SRi (hatchback). Since Christmas 2010 I have had a little problem with the electric windows, they’ve opened twice while parked and locked outside the house. The first time it happened I was more concerned about the contents and interior of the car (had snow blown in) to notice if the car was still locked or not. I just blamed the keys themselves in my pocket (coins or another key pressing the button) for opening the windows as the key can open the windows by pressing and holding the unlock button and the door locks will unlock first and then windows will open, once you let go of the button the windows will stop at that point. The next time it happened I did notice that the car was still locked and the windows were opened to the same point as the first time (about 4 inches from the door sill) which got me thinking there could be more to this. An accidental opening by the key to the same point is too much of a coincidence! Has anyone heard of Opel’s doing this; I do recall a few years ago Audi A4’s and TT’s doing things like this...
I’m now concerned the car will open the windows while parked in a street or at a shopping centre...