The comment field is somewhat special as it has a language token plus another specifier that allows further differentiation, e.g. there are fields like
COMMENT ITUNNORM or COMMENT ITUNPGAP and so there could also be a field COMMENT ID3V1 COMMENT.
MP3tag keeps these differentiated fields, see here:
So any other application that can deal with multi-value fields should be satisfied to find several COMMENT fields. Explorer cannot.