Are you seeing fields that actually have "John Zorn; John Zorn", or are these calculated fields, or expression columns?
Look at a given tag in Action Window > Tag.
MC is now treating semicolon separated items in Artist, Genre, and a couple of others, as multiple items. It used to treat these, for the stated fields, as a single value (the semicolon was just an ordinary character).
Yes, the tags have actually changed, but in a seemingly random fashion.
ALL of my "John Zorn" albums have always been "John Zorn" in Album Artist (Auto). Just one album (of over 100) is now showing as "John Zorn; John Zorn" in both my "Artist" view and in the tags. I only noticed it when scrolling through my Artist thumbs (scanning for strangely missing album art ironically) and I saw two "John Zorn" entries. I expanded the thumbnail size and up popped "John Zorn; John Zorn". The tags confirmed this.
I scrolled around and found a few others exactly as above. "Peter Gabriel; Peter Gabriel".
For what it is worth, each one was missing art I could only restore per my post above.
Lastly, there are actually a bunch of these "missing art" albums. Reimport doesn't seem to do the trick. And every last one has a folder.jpg It may be two totally unrelated problems though.
Thanks again for the help,
Patrick