The Bluetooth has been a mixed bag with my 2012 Mazda3. First off, iOS 8 actually fixed a Bluetooth bug that started with the iOS 7.1 update. The turn-by-turn directions would cut off mid-sentence, unless streaming audio was playing at the same time. That now works fine.
But, I have noticed that the transition between streaming audio and phone calling now doesn't always go smoothly. When I take an incoming call or make an outgoing call, the car would drop the audio stream and go back into search mode for Bluetooth device. It only takes a few seconds to recover, but there is a delay between when I answer or place the call, and when the call goes back over to Bluetooth.
And last night, another weird one. I had a song cued up on YouTube, and after the obligatory video ad played, the audio stream dropped and the car went back into search mode. When the car picked up the audio stream for the music video, it reconnected AS A PHONE. The audio sounded horrible. I closed out of YouTube and tried it again, and it played just fine as an audio device the second time.
At least with my setup, the iOS 8 Bluetooth seems trigger happy about dropping audio sync if there's any momentary break in the program (e.g., a long break between songs or videos, transitioning between streaming audio and a call, etc.).
I haven't tried anything like deleting the Bluetooth profile. Maybe I should try it and see if that fixes anything.