Update: I don't know if this helps, but the "Now Playing" list had the extra entry in it, too.

) I removed the CD above without ripping it
The main display cleared (ie no tracks showing)
The "Now Playing" did NOT clear, it was still showing Track01.cda, etc. - AND it was still showing the "extra" track 13. F5 did not fix this
) I put in the same disc. When I clicked on the CD node, the track list came up correctly (no dupes)
BUT the Now Playing still showed the bogus extra Track 13 (from the previous rip)
) I clicked on the bogus track, and it played Track 13 from the actual CD, not the ripped track from the previous CD

Hope this helps narrow things down.

Fortunately, got distracted and left the system as-is overnight LOL

Yes, F5 cleared the extra track. Will watch for that in the future, and report if F5 does NOT fix it.

Sounds like https://www.ventismedia.com/mantis/view.php?id=16717

Does pressing F5 before the ripping fixes the issue?

And again (new CD each time) - except this time, it's track 13, and the extra Track 13 is Track 13 from the last CD I ripped ... complete with metadata.

Just happened again ... Track 4 this time (new CD)

Ripping a CD on MMW 5.0.0.2256, the liner notes listed 12 tracks, MM showed 13 in both the CD track listing, and the subsequent Rip dialog. MM showed duplicate entries for one track, both were called track07.cda

I wasn't sure if it was an extra track on the CD, a MM issue, or what, so I ripped all 13. Listening to see what the reality was, Track 7 was indeed ripped twice.