I setup bluetooth in both my cars over the weekend. My wife's with a Parrot MKi9000 and my car with a MotoT605. I've been taking her car to work this week and Pandora (or last.fm) randomly loses A2DP after a song is finished. Sometimes it takes 30 minutes. Other times it disconnects after every song. A few times it disconnects and then quickly reconnects. Most of the time I have to switch the input on the mki9000 from bluetooth audio to bluetooth audio, and then do it again and hit play.
I was hoping it was a pandora bug, but last.fm did the same thing. I haven't played around with my car enough to see if it is the phone or the receiver.