Setting [Album Artist] will change [Album Artist (auto)] field's "condition" like lise said and is used to override value in [album artist (auto)] which is calculated from albums [Artist] field
example:
album has 2 tracks where track 1 artist is "Miles Davis" and track 2 artist is set to "Miles Davis Quartet"
[Album Artist (auto)] = (Multiple Artists)
now set [Album Artist] = "Miles Davis" and [Album Artist (auto)] changes to Miles Davis
Exactly. Thanks. I didn't want to get into explaining that, as I was too busy reading posts from as far back as v11 to figure out how Album Type worked.
I'll share the results of that research here for anyone else wondering about it.
Turns out that the Album Type is a hot potato, and has been since v11.
So it isn't a bug, and it isn't exactly clear anywhere how the logic of it works either, but I was able to determine a few things.
Seems that Album Type is strictly bound to the Artist field (unlike the Album Artist (auto) field which can be overridden by manually typing something in the Album Artist field.)
However, it all depends on *how* the artist field is entered.
If you use semi-colons in the Artist field (e.g., Joe; John) the Album Type remains "Single Artist"
But if you have Artist: Joe for 1 track, and Artist: John for another (in the same album of course), then Album Type switches to "Multiple Artists", *even if you have Joe and John in the Album Artist field*.