MP3 Diags (home page - http://mp3diags.sourceforge.net/ ) detects and fixes issues in MP3 files.
While the program is pretty close to feature-complete, not every option for every field that may appear in an MP3 file is currently supported. The implementation of some features is delayed until there is a need for them.
Version 0.99.02.012 adds support for UTF-8 in ID3V2.4.0. This should eliminate the Support note "k" in some cases. (There is another unsupported format that will still generate this note, until there is some evidence that somebody actually has files using this format.)