I just tried with v2.39 (was 2.37b) but Ctrl+R and then Ctrl+Z (delete tag and undo) doesn't work either. I use WinXP SP2 Dutch version and mp3tag mpeg settings are: Read: all 3 checked; Write:ID3v1 ID3v2 checked, button at ID3v2.3 UTF16, Delete: all 3 checked.
I also found now that and mp3 file, made by itunes (v6.0.5, right click convert to mp3) from a m4a file has the same problem in showing the remark field with Win Explorer. Such a file has only a ID3v2 tag. If I look at it with mp3tag everything looks fine, the comment is displayed allright. If look at the tags, alt+T, I see 3 comments; COMMENT, COMMENT ITUNNORM & COMMENT ITUNSMPB. I suspect the trouble has something to do with those last 2 tags. I can remove them with mp3tag, but it doesn't help.
Until now the ONLY way to get a 'good' ID3v2 tags on such file, that shows the remark in Win explorer, is to complete delete the ID3v2 tags and make new ones (or copy from ID3v1) in winamp.
This does NOT work in mp3tag; Delete (with tags mpeg delete id3v2 checked) and Write again ( tags mpeg write ID3v1 & ID3v2 checked), the remark stay unvisible in Win explorer.
Is there a way to refresch the tags in mp3tag? Delete all old incomplete or not used tags and paddings.... only keep the remainig good tags, maybe the best way is to complete rewrite the tag section it will take longer but it will be cleaner and maybe work alright.