Great investigating by Kirk McElhearn.
This is embarrassing. No wonder people have had so many problems and so much data loss with Apple Music’s cloud-library features.
It’s as if nobody who made this implementation decision had ever encountered remasters, re-recordings, clean versions, live performances, or the many other extremely common reasons why two very different audio recordings might have the same artist and title.
What’s even more puzzling is that iTunes Match did this much more correctly using acoustic fingerprinting, and for whatever reason, Apple Music chose not to. And if you’ve activated Apple Music, it seems to override iTunes Match similarly. (Update: This may have been “a glitch”.)
I highly recommend disabling iCloud Music Library and migrating away from any reliance you have on iTunes Match. You can still listen to Apple Music without them. Don’t let these cloud-matching “features” anywhere near your music collection.