This is mainly aparent with Rebound, but could apply to all applications.
You play the game for a while and then stop and do something else...
After a while the game music starts up again without you accessing it...
This is to do with things not being able to close properly, ultimately an issue with the Smartphones multi-tasking environment!
For Rebound: [thanks moorejam!]
Pause the game first, so you go back to the the reset game menu, and exit from there. This seems to prevent the problem.