OH! No, the seatbelt isn't clicked in... it's completely undone...

Here's a photo of a different back seat...



You can see that the seatbelt originates in the actual seatback and it ends in the bottom of the lower seat cushion.

When the seat folded down, (while the seatbelt was unclicked), for some reason, the seatbelt locked. Now when you lift the seatback, the top of the seatbelt is locked, and it pulls up on the lower portion of the seat...

I'll try and get a photo of it on my lunchbreak...

I may have to take it to BMW... grr!