Custom parts with a / in the title disappear.

I've been creating custom instrument parts for my latest project. Unfortunately, any of the custom parts that have a / in their name in the parts manager (such as Violoncello/Contrabass) disappear entirely when MuseScore is closed and the file opened again. This is a frustrating waste of time - as all the work I had put into engraving has vanished. Note that the part does not disappear or corrupt on saving, only when the program is closed and reopened.