Tip to whom it may concern
There is a tag field MOOD to specify the character of the song in mp3tag.
In Windows Explorer is an option to display tag info in content pane by selecting appropriate info fields for columns.
If MOOD field is filled with mp3tag and MOOD is selected in WinExplorer it will be displayed blank.
MOOD in WinExplorer corresponds to COMMENT MUSICMATCH_MOOD field in mp3tag