If you unset musicbrainz_recordingid via scripting and use Scan on a song which is slightly mistagged (e.g. uses track number and track name of a different track from the same release), it will not be correctly moved to its respective spot in the right pane according to the Scan, but actually according to its tags. After enabling musicbrainz_recordingid and scanning the files again, the tracks will be assigned their positions correctly based on the scan result. Attaching screenshots (one with musicbrainz_recordingid and one without).

Edit: Found out that the track doesn't necessarily have to be mistagged, it can also just not match any of the track titles from the release it's been matched into. Having a track title written in a different script is enough for it to be assigned to a different track within the same release which does not match its AcoustID. Apparently it picks a track with a title closest to the title of your track. Attaching two more screenshots.

So it looks like if you perform a Scan and you have musicbrainz_recordingid tag unset, the track gets matched to the respective release by its AcoustID, but to the respective recording by its tags.

Edit 2: If you clear the Artist tag, the track still gets matched to the album that contains the track with the matching AcoustID, but instead of being misplaced, this time it gets moved to the "Unmatched Files". After enabling the musicbrainz_recordingid again, the file gets properly assigned to the track with matching AcoustID. Attaching two more screenshots.