I just had a conversation about this with my friend today.

He had the same problem in his '89. (According to him) the seat backs only lock on one side, the side where the pull handle is. Drivers seat on the left side, passenger on the right side, but they have teeth or whatever it is that locks, on both sides. Swap backs, and now each seat will lock on the gear(or whatever it is) that was never used before.