I stumbled across an album I have that uses the .fla file extension for whatever reason instead of the usual .flac and mp3tag does not process these file types by default. I added .fla to the list of incoming files in the options and now I see them in the file list. However, mp3tag does not recognize any tags in these files. If I rename them to .flac, mp3tag can see the tags just fine.
You can only remove file extensions from this list to restrict incoming files. It's not a bug, the *.FLA file extension is simply not supported by Mp3tag and I suggest renaming the files with the default file extension for FLAC files.
Hmm, I don't think the list works like this. The list is a whitelist, meaning it only matches filetypes that are IN the list. If its not on the list, it doesn't get included. Compared to a blacklist where if its on the list, then its NOT included. I was able to add *.fla to the list and see the .fla files in the mp3tag window, but the tags were not visible. Yes, changing the file extensions to *.flac worked and I was able to work with the files. I just want to make sure we are clear on the bug report.