I also found that the song I wanted was no longer staying selected - the Aquarium was reverting back to the guitar. I seem to have fixed that by removing guitar from the list in music. I hope I will be able to put it back when I want to use it again
All of the songs that are in the list will play. I think in version 10d, they just play in order. But in the latest version (11i), there is a checkbox to make them play randomly.
The only way to get a song to not play, is to remove it from the list. If you want to get the CanonGuitar.sgt song back (after removing it), ask in this forum for instructions - it's not obvious.
(JohnWho - consider putting instructions in the readme).