I agree that this is because the replacement screen assemblies let too much light through the prox sensor hole. The aftermarket prox sensors are probably less sensitive, which is why they are working. Something to try that worked on older iphones: use a piece of black tape (or scotch tape sharpied black) and poke a very little hole in it. Then place this over the prox sensor window on the phone assembly. Haven't had the chance to try this but will later this week...