Default stock android 4.3 nordic: bluetooth problems

Hello everybody,
I'm running the latest stock Android 4.3 on a rooted Note 2 with CWM installed. What happens is that when I use the phone to make or receive phone calls (streaming music is ok instead) in my car (but I experienced the same problem in another car) the Bluetooth all of a sudden goes off and I need to either turn the screen on or toggle the bluetooth button.

Any idea on how to fix it?

Thank you,
Davide