Both driver and passenger seats simply fold down and don't lock into position when passengers are entering rear seats. The tab on both seats in the rear seem to be working but seats don't lock in selected position. No real concern when sitting in seat but someone tell me there is an easy fix or is it just to common!

 

I don't think they are supposed to lock unless the car hits something. The tabs on the backs are there to override the inertia pinion thing. Jack the rear of the car up or park on a steep hill facing down and try again. The pinion should lock them in these circumstances