Duplicate parts?

I was working on this transcription and ran into some trouble once I added a new piano part called "2nd X Only." When I look at the list of instruments, the right number of parts appears, but when I click "Parts," there are duplicates (which I labeled "[name] OOPS?" though I'm not sure which is original and which is a rogue copy). I'm trying to make a part that shows both "Backing Vox" AND "2nd X Only" (I made them separate parts to make it easy for me to play each one back in isolation) and whenever I try, MuseScore crashes. Help me find the bug? Thanks!