@Loki, I found another bug with the music boxes.
Was collecting them today, and making copies for ones that are used to make the title and tutorial boxes. I was trying to copy the Ocean music box. Started playing the one I already made, equipped a new music box to record it. A minute later I check...
...and the equip slot is empty. The music box has vanished.
So I get another new music box, equip it, and try again. Same thing happens: I check to see if it's recorded the music and find instead that it has vanished from the equip slot. Deciding to try another tactic, I flew all the way across the map to the ocean, equipped a third music box, and tried to record a fresh copy. But again the music box disappeared.
I ended up exiting and relaunching the game, which made the music boxes work properly again. But three of them still vanished without a trace on me.