At present the 64,000+ files for my Music Collection sit on an External 8GB M2.SSD that I can attach to either my Win or Mac machines and since I'd updated a lot of metadata for those files, using the Win PC, I decided to clear down the Mac Library and then Re-import the files.
This is a mistake. If you have previously imported files and the internal tags have changed, you do not need to import them again. Just highlight the files and do: Library tools > Update library (from tags)
That will re-read all the tags in the files and update/add any relevant tags. That's it. I believe running auto import on the files will also update the library based on new or changed tags, but not 100% sure about that. I'm definitely sure that the procedure above works every time.
This I did in "Files View" and for some obscure reason MC would switch between telling me they were on 1 Volume and sometimes on 2 Volumes.
When it was saying 1 Volume it was correctly reporting the volume name preceded by a forward slash but when the 2nd volume appeared the volume name was preceded by a back slash.
I'm not sure how this would happen, but I believe you. I think that if you stick to a library created on the Mac and do not reimport, you should be fine in the future.
When I ran multiple versions of MC I did something quite different than any of this: I did a Library Backup on one system and then transferred it to the other system. Then did a Library Restore. Finally, I fixed all pathing issues using Rename, Move, and Copy Files with the Find & Replace option to fix the initial drive paths. That may or may not yield good results for you. Give it a try on a throw away library and see if you like it. This way the two libraries really are the same since one is built from the other.
Good luck.
Brian.