I realised this just now when I tagged some files with MusicBrainz Picard and then tried to use another websource using data from MusicBrainz.
Apparently the tag field mappings used by Mp3tag are a little out of date compared to what MusicBrainz uses now.
Files tagged with Picard look like this:
Currently it's kind of a pain to work with both Picard and Mp3tag (I have to use Picard for the scanning from time to time which is why I never noticed before)
THis is how the web source script writes the tags.
There is no "mapping".
MP3tag displays theses field names:
The standard ones as suggested by the standard
The user-defined ones that you used
The ones that you used for manipulation and got imported e.g. by a web-source.
If you reset the field list e.g. in the Convert-Tag-Tag function (click on the button with the right-arrow and select "reset list"), you will see that the non-standard field names are gone.
IMHO this is not a bug but a request to modify the web source.
I was about to create a topic about my problem but after some thoughts it might be linked to what you reported...
I wanted to tag an album of Air using the import tool for MusicBrainz. It worked all well, except it didn't import the year nor the cover of the album, which i found suspect, as it's quite a well known album.
So i gave a look at the web page from which the tool had imported the tags (here), on which you can see the release year and cover are preset. So i guess this problem comes somewhere from MP3tag, perhaps from where Mihawk90 pointed at !
