Pretty much the title. Any of the songs that normally play don't.
I found that the cause of this is probably the way the map plays the music. It's based on soundscapes rather than ambient_generic entities, like most maps. I'm assuming that the reason it uses soundscapes is to have players hear separate songs, based on their location. I could fix this, but I'd make the songs the same for all players.
I'll notify you guys if I make any progress.