Music isn’t cleared on loading a module. This means that music from one mod ends up in another mod simply by loading the new mod. This only affects mods with no music.
Thinking about this more I don’t really think it’s a bad thing and most of the time desirable.
It’s really bad, actually. It can inadvertently cause Copyright infringement for distributing music when you publish a mod to which music was inadvertently added.
Thanks for the feedback I’ll add that and way to load music from another save when you expand it.