Several types of changes in scores do not get "detected" by the program
Whenever there are changes made to a score, the program sort of "detects" them and shows an asterisk to indicate that the score has unsaved changes. However, some changes such as modifying the volume of an instrument in the volume mixer, or inserting a special character into lyrics go unnoticed and the score could be closed without any prompt to save any changes, and there will also be no way to undo those changes other than closing and reopening the score.
It could be saved if the save button is pressed but it would appear as if nothing happened. But, just as said earlier, even then, the score could be closed with these unsaved changes if not manually saved previously.
A related post: https://musescore.org/en/node/23808
Comments
I think the Mixer issue is known, see #22802: Mixer settings are saved in file but score not dirty when settings changes. Been around a while too.
But as for other things that don't mark the score "dirty" (the technicalish term for this), I am not sure we have any record of specific issues. I can confirm that adding a special character to lyrics does not. Not coincidentally, It also doesn't undo properly - that's actually we track whether a score is dirty or not (if there is something to undo). Can you submit a bug report on this to the issue tracker (see Support menu above)?
Same for any other actions you find similar issues with.