I've got a 2 month old ST and on 2 occasions now when the car is frosted up the drivers door will not close. It just bumps open again as if there is nothing for it to latch onto. Turn on full defrost for a couple of minutes and it works fine. Any ideas please ??

Sounds like the latch is frozen stiff.

Your best bet is to get it back to the dealer and get the latch changed under warranty.

Its just that the latch isn't returning after you open the car. The grease that may already be on there is solidifying with the cold and therefore not acting as a lubricant. Try some WD40 around the door locking mechanism/latch/catch, to see if that improves things.

It used to happen a lot on an old Mondy I used to own, never seen it happen on a new car though.

like they've said, get it sorted, poss under warranty

If desperate/rushing try getting in the car and holding the door shut then using the key to lock the doors :)

Sounds like probably no grease in there and water droplets freezing casuing it not to return. Make the Dealers sort it out.