Major Issue !!!

[330i2X5]

I came across a problem today...( only been a few days I had this beauty ) that has me worried..heres what happened:

Arrived home on driveway which is sloped a little uphill.....parked...left engine running and put into "P" park.
Got out of vehicle, opened garage door, came back to X5 and shifted to "D".
Just as I give some gas to move, the gear shifts by itself to "P" PARK !!!!!
I tried it 3 or 4 times and same thing !!
Then I decided to put it in reverse and see what happens....SAME THING...except second time I did it, it allowed me to reverse but as it is reversing it shifts to "P" and an array of grinding noises....obviously as vehicle is on the move in "P" mode....!
I then decide to switch off vehicle.....lock....then unlock get back in and restart and then try again and 2nd time round vehicle begins to move forward and I successfully park in garage !
I had no handbrake on by the way !

I HAVE ABSOLUTLEY NO IDEA WHAT IS GOING ON??? I checked if it has anything to do with Start Off assistant but there is no mention in manual of car moving to "P" to prevent any roll back...just that you must within 2 seconds move off otherwise vehicle may roll back.

Im thinking now what happens if I drive this and during higher speeds it suddenly shifts to "Park"....dire consequences to transmission and engine....anyone else???