I was importing this release : 
https://www.discogs.com/Various-Homegrown-Cupboard-Music/release/53638

Into musicbrainz and noticed some sub-optimal behavior with regards to the recording search on the "Recordings" tab of the release editor.

Briefly :

1) all of the recordings on the release were already in musicbrainz, because the release is a CD compilation of tracks from previous vinyl releases
2) because the existing recordings are all from vinyl, their durations are all (?:??)
3) perhaps because of 2, none of them are returned in indexed search at all
4) when I switched to direct search, they would be returned. however on track 7, "Black Cat," the results did not appear to suggest a constraint on artist name... so after being unable to locate my release in the first 7 pages of slow direct search results,  I gave up and just copy/pasted from the release page for the vinyl release.

In summary :

• It is unexpected that indexed search does not return "exact artist-name+exact recording title" matches under some circumstances. It seems especially odd because on the recording tab the artist-name constraint is already hydrated with a mbid.
• It is unexpected that direct search does not return "exact artist-name+exact recording title" matches first.

As an aside, I wonder how many duplicate recordings I have personally created as a result of encountering this case...