Part versus Instrument
There are several places within MuseScore where the term "part" and "instrument" are used interchangeably, other places where a distinction exists. Also, the relationship between either of these and a "staff" is not always clear. This probably needs to be cleaned up.
Here's my understanding.
Staff - what you actually see on the score. The top "Staff Properties" portion of the "Staff Properties" seems to be correctly labelled in that these settings affect just the current staff. These settings include the staff type, size, and line color & visibility.
Instrument - an abstraction that defines a set of one or more related staves that can be assigned additional properties as a group. The "Part Properties" section of the Staff Properties" dialog should probably really be "Instrument Properties" as these settings should affect all staves for the current instrument, but not necessarily all in the current part. This includes the playback sound(s) that appear in the Mixer, the long & short names, transposition, and usable range.
Part - an abstraction that defines sets for one or more related instruments that can be displayed as a separate score in a tab alongside the main score tab. Normally, each part contains one instrument - this is the behavior of the "New All" button in File / Parts. However, you can manually define parts containing multiple instruments. It occurs to me this could be useful to define temporary subsets of staves to work on (like just the strings in an orchestral score). The only really relevant part attribute is the title displayed on the tab.
If this understanding is correct, then I think there are a couple of things off:
- the "Part Properties" section of the "Staff Properties" dialog should be renamed "Instrument Properties"
- the "Part Name" field within that dialog should probably be renamed "Instrument Name", and the behavior should be changed to only affect the current instrument (see below).
- Currently, the tab for the part is labelled using the "Part Title" from File / Parts, but the part itself is labelled using the "Part Name" (the field I say should be renamed "Instrument Name") of the first instrument included within the part. I think the Part Title should be used here as well. When generating parts automatically via "New All", this defaults to the "Part Name "(sic), so its only multi-instrument parts that would be affected by such a change, I believe. Otherwise, you end up with your "strings" part being labelled "Violin I".