Instrument names not sticking

I am working on a choral score with three alto staves: alto - when only one is required and alto I/alto II when divisi.
I have discovered that getting the correct label requires me to edit the labels whose default is Alto, Alto 2 and Alto 3 by editing Alto 3 through Alto in that order. If I attempt to modify the names from Alto 2 nothing changes.
Additionally, I have found that even after saving the file, on opening, the last flow has renamed the instrument labels back to their defaults. This is very frustrating and remains so until I start a new flow.
This behaviour is a bug?
PS (still waiting expectantly for musica ficta)

I suggest you try adding a leading space to the name of the Alto instrument held by the player whose name should remain unnumbered, so that the singular full name is " Alto" instead of “Alto”, and that should be the only renaming you actually need to do.