Although I can't say I KNOW the answer... I just got the Pionneer AVH-4100NEX installed by Mickey Shorr (local shop). I am having an issue with my radio playing Bluetooth calls. BT Music works without issue, but no calls.
I had placed a call to CS and they had me play FM radio and move the fader to the FRONT and I lost all sound, moving it to the rear I heard normal music.
He said that I have a 2 speaker set up and the speaker leads need to be moved.
Hope that helps