Default P710 bluetooth problem

so i was wondering what may cause problems with my P710 bluetooth.
using the stock rom version V10J_00 completely disables my bluetooth. trying to turn on BT doesnt work at all.
so today i installed the modded kitkat version for P713 and my bluetooth works fine.
reflashing stock images kills bluetooth again.

so id like to know which files effect the bluetooth.
can anyone give me a hint what may cause that problem?