For Release [r6311887], when I import the tags the tracks, listed as A and B on Discogs, appear as 1 and 2. The titles don't get added at all. In the "adjust tag info" window, they appeared with "TEMP_ title" tags
When I went to "edit release" I found that there were two extra blank tracks, which did not appear in the release as displayed in Discogs. (You can see this in the edit history). I deleted those, and then the release imported correctly.
While this is a data error in Discogs, MP3tag didn't deal with it gracefully.
I suspect similar issues in other problems I've seen lately (I've been doing a LOT of imports from Discogs for 7" discs.)
Mp3tag already has a lot of workarounds for malformed input, but I don't want to cover anything that's possible.
Glad it's working now, the best way is to correct those entries.
If you find something that cannot easily be corrected and might be a bug in Mp3tag, please let me know.
Given that Discogs is an important source, the Discogs default is to have 4 tracks so singles depend on someone doing the right thing manually, the error isn't visible in the base Discogs UI, and MP3tag knows there's a problem and is dealing with it poorly (it's creating those "temp_" tags instead of ignoring empty default tracks), it seems like something that should be addressed.
Easy for me to say, of course. Maybe easier for you to do now that you've updated the Tag Sources code? (Just verified that the problem still exists in the latest version).