Unfortunately, it looks like seat back collapse is/was a known problem across the whole industry... at this point I'm trying to find out if the requirement (FMVSS 207) has been upgraded since it was written in the '60's. As of a 1999 LA Times article I found, it was being considered at that time - but I'm not sure if it ever was.
My understanding is that the gear teeth in the power seat mechanism are not strong enough to withstand much force. I read that some seats have failed at toll booths when people put extra force on the seat digging for change in their pockets... again, all makes and models.
My back is sore but my neck hurts worse - as the seat fell back I had no neck support and my instinct was to try to stay upright - so I strained all the muscles in the front of my neck - so much so that it still hurts to swallow.
Unfortunately I was pushed into the truck in front of me and when I did I slid forward and into the dash. If I had been upright that would not have happened...
2003 Marauder - 300A
Superchips 1725
1969 Mustang Sportsroof
302, 4 speed, 3.40 trac-loc, Edelbrock goodies, electronic ignition,
1991 Mustang GT Convertible
Stock 5.0 short block, Paxton 1220 SL w/ 10# pulley, 489 RWHP/472 RWTQ, many other go fast & handling parts