Archived:MIDI sounds from MIDlets in background not stopped on S60 2nd Edition (Known Issue)
The MIDI sound playback is not stopped if the MIDlet is moved to the background. If the Application key is pressed while the MIDlet is running, the MIDlet is left in the background. If a MIDI sound has been playing, it continues playing even if the MIDlet is not visible. There seems to be no easy way to track if any of the Displayables are visible or not.
This problem exists in Screens such as Form and List, but not in Canvas. In Canvas it is easy to track whether the Canvas is visible or not by using the hideNotify() and showNotify() methods. Such methods don't exist for Screens.