Edited parts are not marked as dirty, saving a part marks score as clean
Scores without linked parts
When a file is edited in MuseScore an asterisk is added to the end of the filename displayed in the score tab. This marks the score as "dirty" (i.e. it shows that there are unsaved changes). Saving the file (with "Save" or "Save As") causes the asterisk to disappear, because there are no unsaved changes (the score is "clean").
Scores with linked parts
When a score has multiple linked parts, and only one of those parts is edited (e.g. by changing the horizontal or vertical offset of an element) then the entire score is marked as dirty. The part itself is not marked as dirty.
If only one part is edited then only that part should be marked as dirty. The entire score should be marked dirty on the top row of tabs, but not the "score part" (leftmost part) on the second row of tabs. Edits which affect all parts (e.g. changing a note) should mark all parts as dirty.
Saving the part (by going to File > Save As) saves only that part, yet the entire score is marked as clean, even if there are other parts with unsaved changes.
If only one part is saved then only that part should be marked as clean. Or, at the very least, the score itself should still be marked as dirty.
Why is this important?
Some users have lost work as a result of using "Save As" on a part and not realising that only that part is saved. Worse, they may have overwritten the full score with the single part, meaning that all the other parts are lost entirely, rather than just the work from a single session being lost.