WMP11 shows still a "Composer" after MP3TAG run

Even when I run the mp3tag and remove all tags, after looking in wmp11 "Advanced Tag Editor" it still lists a "Composer", an incorrect one too.
Is there no way to strip a mp3 file really clean or why does it happen?

Not sure on this one, but WMP might somehow save these settings it gets from id tags in it's own files. Did you add these files to WMP before you stripped them, meaning ever added them in the first place with these tags already filled in? I have the same problem with genre, whenever I clear the genre for songs I have added to WMP it keeps recreating the ones I had before I cleaned them.

I should try to add a song that it's never seen and see if anything comes up. After a certain time of being in the library add a tag with some info and erase it from the library. If said song were stripped then added to WMP again with those portions filled in then it must be the player.

Used to be my problem with WMP... Just remove the file from the library and then add it again. It works for me.

or maybe... your WMP library option is set to "Overwrite all media Information". means that tag data is replaced by the one downloaded by the WMP (which could be wrong!). You should just select "add missing info" or just disable this feature.