Well yours is truly beautiful and I'll be staring at that picture until mine comes in!
When will it get to your hands?
- - - Updated - - -
In every case I've heard of the "abrupt unexpected shift to park while in reverse" it is this butt liftoff issue. Try not lifting your posterior off the seat when you turn around - the easiest way to do so is not to brace your right arm on the passenger seat but keep both arms in front of you. This is actually a better way to backup. My driving instructor many years ago told me that if you brace your arm on the passenger headrest during your driving test it is a 5 point deduction in New York state.
I can't remember when I took that DMV test. So many moons ago. Thanks for the tip