I've configured the main window to show me the "Sort Album Artist" and "Sort Artist" fields. It appears that all of my tracks have those fields completed, but I know that many do not. When I click to edit tracks, I find that many don't have this information. So, apparently, MusicBee is showing me those fields populated with data from the Album Artist and Artist fields.
Per a suggestion from scampbll, I tried searching. When I search for Sort Artist or Sort Album Artist and look to match <has no value> no tracks are returned by the search, even though I know that many tracks don't have any data in Sort Artist or Sort Album Artist (and I checked to be sure...).
So, I guess my request is:
1) Allow MB to return search results for Sort Artist & Sort Album Artist when those fields have no data and/or
2) Allow a user to turn off having MB automatically populate those fields in the main window display when those fields don't actually have data.