I also experienced something similar i think; I was adding a release. then when selecting recordings, for one i chose an excising recording. however later after looking more thoroughly i decided it's better to create a new recording jut to be sure (this is classic music )
however after going to the final screen it shows as having attached (and not with a grey/lined text with alt: "this will be created" etc)
going back to the recordings tab shows it as attached to a recording (and not the previously chosen one, a different one)
going back and forth after re-setting as "create new recording" yielded all kinds of unpredictable results that also bleeded into the track/recording above it, eventually managed to fix it ,but it was very frustrating.
I am wondering, is there a way to check how many tracks/recordings could have been affected by this bug? I don't know how many people are editing via the beta site, but if I experienced it 2 (or maybe even 3 times, because I had to fix https://musicbrainz.org/recording/bc8929b6-1eb2-4b51-bf36-b6317db15fda as well), I wonder how many times it could have happened to other people. There's also https://tickets.metabrainz.org/browse/MBS-9710 which might or might not be related to this bug...