Phone calls with BT and headset outlet used at the same time

[zalozhed]

I turn my BT on and connect Mogul to MP3 outlet using the standard splitter (miniUSB/2.5 mm) to listen some music in my car. When I receive a phone call it first comes through my BT for 2 sec and then switches to the car speakers (another words - headset outlet). The same happens if I try to make a call. My only solution for now is to unplug a splitter and then answer a phone call.
It doesn’t seem to be a BT set specific because I’ve tried a few already.

I have 6.1 stock ROM and looking for help to resolve this issue.