Re: Problem with Safety belt in rear
Funnily enough, my 156SW is at the stealers today getting the rear-centre belt replaced under warranty - for exactly that reason.
I think the belt was actually jammed when I bought the car (a couple of months back), but after a spot of jiggling, I folded the seat flat - and couldn't lift it up again, because the belt retracted even further and jammed the seat in the folded position. I ended up having to lift the seat back halfway and unbolt the bottom of the belt from the floor using the wheel wrench (thankfully they're both 17mm bolts... :-) ).
Talking with the technician at the dealer, he thought it was one of two things - either the inertia reel itself, or the mechanism used to control the slack on the centre belt (which is tied to the lock/release handle that drops the seat back) was knackered.