Hi Jim, sorry for the lack of information. The reason there isn't more, is I'm not sure what information would be relevant.
But your method revealed some interesting info. When I click save, MusicBrainz Picard acts as if the data has been written, but the modification time doesn't update. I know it's the same files, cause what I right click -> open containing folder, it refers to the same folder as screenshot 2.
Thanks for the help/interest in the question thus far.