I'm having a similar problem with my Motorola Q9c and f700BT combo. The only way that I can get the sound back is to either shut the car and restart, or to shut my phone. It looks like even though the phone hangs up by either using the button or hanging up on the phone directly, it looks like the 700 doesn't "let go" until the bluetooth connection breaks.
Any suggestions.
I am a total newbe to the site. Thanks in advance for pointing me in the right direction.
Also, I picked up the bypass rewiring from another post on this site. Sweet!