cold transmission
 

Whenever my car is cold there seems to be a "slide" when the automatic transmission changes gear from second to third (or third to fourth, I don't really know :-) ). The engine revs up for a while and then the gear engages. This happens every time but only once - the first change when the car is still cold. Each next change is smooth and quiet and the car drives like a dream. What could be the cause of this? Can I just ignore it and enjoy the drive?