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
Editing
Current behaviour:
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.
Expected behaviour:
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
Current behaviour:
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.
Expected behaviour:
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.
Comments
I have posted a feature request to add "Save Part As" (or move part extraction to the Export function), which might serve to alleviate/solve this bug: https://musescore.org/en/node/272925
I believe I just experienced this bug. Woke up this morning and got back to work only to find that every instrument except one was missing from my score. I must have saved while working on its part last night. I'm starting from scratch - lost days of work.
I think what you are describing is something different. Saving while working on a part is fine - it saves the full score. This issue is about what happens if you use save as", not ordinary save. And even "save as" is mostly fine () as long as you don't give new file the same as the original, and then when you are warned that this is going to overwrite the original, ignore the warning and do it anyhow. Unless all those things happened, then your score is presumably still there, you just may be looking in the wrong place.
(*) I say "save as" is mostly fine, because as this issue says, it does mark the score clean, meaning if you don't save again, you will lose any work done since the previous full save. But you should still have a full score and parts, which is why I suspect you are simply opening the wrong file.
Also, even if you did overwrite the score with the part, it's often possible to get back to a previous version, if you are saving to a folder on OneDrive, Google Drive, Dropbox, or are using Apple's "time machine" (not sure how that one works).
Came up again https://musescore.org/en/node/318391