I KNOW mine does not have auto-levelling. If I park my tail in the back seat (with front seat properly forward), it stays down.
As I am not with you to perform this test, simply substitute twenty-one and two-thirds stone for me to replicate this test on your own.
The writer of this message is not responsible for any back seat damage that may occur, nor do I know where one can find said stone.
PS -- Now we know why my E430 may be a bit slower 'n yours -- I am in it usually.