That or the music changes in certain levels, because look at this:
http://www.youtube.com/watch?v=2gjVD_1ej8w Aha! I was right! Look, music has changed! This is the town from MPO, look at the town online on MPO+.
http://www.youtube.com/watch?v=HsFWuPUBlu0So either music changes through old MPO levels or you can change them.
The music changed, atleast for some levels.