"Save as" while viewing a part only saves that part, losing any changes to the score or other parts.

1. Create a score with two instruments
2. Save score with name ORIGINAL
3. Create parts, INST1, INST2
4. Edit the score - note that it is marked "dirty" with an asterisk
5. View INST1
6. Save as with name CHANGED
7. Note that score is no longer marked dirty and the name shown on the score tab is "CHANGED". All parts are still present.
8. Close the score by clicking on the X of the score tab or close MuseScore. Note that it closes with no warning.
9. Open CHANGED
   Result it only contains the single INST1 part. Any changes made to the score are lost as is the INST2 part.

The logic of this seems very flawed. It is too easy to lose work and indeed I have just lost an afternoon's work. I opened my "work in progress version" to finalise it. Created parts, made a few final edits, tweaked the score and parts layouts and then while viewing a part did a save as "final version" and closed MuseScore. Opening "final version" I find it only contains the part I was viewing when I saved it. "work in progress" is as it was before I started work. Except for the one part remaining in "final version" the edits to the score and all the other parts are gone.

I realise that saving when viewing a part gives a way to export the part as a new score but it would be better if that function was made part of the export facility. It currently allows export as an uncompressed Musescore file. It would seem logical to allow export of parts as compressed files and this would offer more flexibility. This would remove the need for "save as" while viewing a part to create that single part file. "save as" should save the whole score and any parts, whatever the user is viewing when the save is made. Alternatively (but surely second best), after saving a part the score should remain marked as dirty if it or any part contains unsaved changes. Closing and losing changes without warning is nasty.

For the record, my set up is OS: Windows 10 (10.0), Arch.: x86_64, MuseScore version (64-bit): 3.6.2.548021803, revision: 3224f34

I don't recall whether earlier versions behaved similarly.