Sorry to bother with what is probably a fairly trivial issue for most people.
Using wma lossless audio files.. and yes 0.465.
Emptying a tag, Genre for example, removes the Genre tag from the file. Verified this with third party tool.
The problem with this is that the MC import engine does not recognize a non-existent tag as a tag change.
Subsequent imports in other libraries retain their original value, even though there is no such tag in the file.
For example, a track with Genre tag of value "Electronic" in library A also appears in library B with Genre tag of value "Electronic". Clearing the genre tag in library A so that it is blank, and importing in library B shows the track in library B as "Electronic". But the file tags show that there is no Genre tag in the file.
Library A & B settings are "Update for external changes" - checked, "Fix broken links: yes". All other library import options off. The Genre tag has "update to file tags (when possible)" checked.
Also, similar results are obtained if there is a pre-existing track in a library whose underlying file has changed (probably by a third party tool), but the timestamps (mtime) have not changed.
For example, a track in library A with Genre "Electronic" is changed to "New Age" by an external process that resets mtime to its original value. Upon import into library A, the track values are not updated from the tags, and Genre remains "Electronic".
In both cases, library tools / update library from file tags corrects the problem.
I can see where an argument could be made that the latter is a design decision that results in unexpected behavior because of a third party tool, but the former causes serious problems (for me) and requires no third party tool.
I really hope that it is easy to fix this. I have many libraries based on the same track set, and doing an update from file tags for all libraries whenever this situation might arise would be unwieldy.