Ok, interesting results. So first off analyzing your files did indeed give some different AcoustIDs. This is the actual result of the fingerprint comparison between the WAVE and the 320kbps MP3:
https://acoustid.org/fingerprint/89447221/compare/89447222
So you see there is some notable difference, but not too bad. It’s reasonable to assume that this is somewhere near the threshold to be considered the same.
I then went on and converted the WAVE to different bitrates, starting at 128 kbps and going in 8 bit steps up to 320 kbps. Also I tried 64 kbps The conversion was done with sox like this:
sox -S --multi-threaded Dj\ Brokdorff\ -\ \(I\ Am\)\ OldSchool.wav -C 320 out-320.mp3
The result is interesting, the fingerprints for all bitrates up to 288 kbps produced a fingerprint more similar to the WAVE one, the fingerprints for 296 and above produced fingerprints more similar to the original MP3 one. I have unfortunately not saved the lookup results from the AcoustID API response, but at least some I saw contained both fingerprints as potential matches, just with different similarity.
So basically we are at a case where the fingerprint similarities are moving just along the threshold line.
Now I did something that actually changed the situation: I submitted some of the fingerprints of the other encodings. If AcoustID finds multiple potentially matching candidates for a fingerprint, that is a submitted fingerprint sits somewhere in between two AcoustIDs in regard to similarity, AcoustID checks whether it is reasonable to merge the two AcoustIDs. And that’s what it did in this case: Track "f7f3ee20-7c6b-462a-9188-73a063605970" | AcoustID