Also sounds like the infamous "transmission slam" try searching for that...

Transmission slam is when the gearbox seems to change into first gear with a thump just after, or as you stop. I have found that it gets worse when I baby the car and the adaptive transmission sets itself into a very relaxed mode and does not select first quckly enoungh when you are slowing down. Thrash it a bit, or drive in sport mode for a while and it may clear itself...