This worked for me:
1. I closed the music app. by double clickingthe home button.
2. the open apps will appear along bottom of display.
3. I held my finger on the music app until it began shacking and the minus sign appeared.
4. touched the red minus sign to close the music app.
5. rebooted the phone (may not be neccesary)
6. Music no longer plays after phone calls, at least for now.