This is going to be a strange bug report, because it was actually several bugs combined, and I'm not sure how to reproduce them, so I'll just describe what happened.
I was adding a new compilation album to MusicBrainz, and so I was associating its tracks with the existing recordings that the compilation re-used.
In the course of identifying which recordings to use, I was also merging some of the existing recordings in cases where I was able to verify their redundancy, and also linking some recordings as being edits of other recordings.
I did this for several tracks with no issue. Then, I got to track five, and tried to link it to this recording: https://musicbrainz.org/recording/9af48dd6-f57c-489c-b32e-fab34f12f58c
However, when I pasted its url into the search field (which, again, worked perfectly for the previous four tracks) I saw this: (see attachment "1_TRACKLIST.png") Notice not only that the recording's name appears as its URL in the 'recording' column on the left, but also it appears TWICE in the 'suggested recordings' list—with two DIFFERENT track lengths! (I'm not certain, but I believe those two entries were actually two recordings which I had marked as one being an edit of the other—NOT two recordings which I proposed for merging, which was my first guess... but unfortunately I didn't write it down so I can't be certain I'm remembering correctly.)
Perhaps even stranger still: when I moved on to the 'edit note' page (see attachment "2_EDITNOTE.png"), among the list of edits summarized for me was an edit to change the name of the recording TO its url, even though you can see that I did NOT have "update the recording title" checked on the tracklist page!
In the end, to work around the bug, I told the tracklist page to make a new recording for track 5, and then merged that new recording to the desired recording after the fact; this seems to have gone smoothly (although we will have to wait and see exactly what happens once the edit is accepted).
For reference, the resulting release is here, in case its history betrays any clues to the bug: https://musicbrainz.org/release/6a8a03db-4c08-4aa0-9a50-9727f9e96fb0