No Music After Monster Despawn?

[MsHannerBananer]

With the exception of like, 1-2 enemies, my enemies don't despawn, so I've never worried about this until recently, when I went back to test some levels and realized that after one of the enemies I do have that despawns after you get an item, the music for the level doesn't return.

I can work out a work-around, but I'd like to know if anyone understands why this happens, and could fill me in?

[Mudbill]

I think I've only experienced the music muting after dying and respawing, not when a monster despawns. I have noticed that sometimes, the music for the monster can keep playing after he has despawned. I don't see any logical reason for this, so I can only assume it's a game bug.