I'm not sure if this could be considered a bug, but it really bugs me.
If I accidentaly select a space before or after the text which I'm copying to any of the tags, it will be saved. For example, if I copy an artist's name from the internet and accidentally select a space before it (very easy to do in a body of text), that space will become the first character of the artist field after saving it, and that artist will show up first when sorting artist names in a list in any audio manager. Also, it's very easy to overlook such things while viewing files in Mp3tag, and it seems to do this for any tag field.
I don't know if there is any special case in which having spaces at the beginning or end of tags would be justified, but if there isn't I would like to recommend changing Mp3tag's default behaviour to deleting those spaces when saving, similar to the way Windows automatically delete them when you try to rename a file.
Other than that, Mp3tag seems pretty much flawless.
I am quite glad that MP3tag does not interfere with my input even it is somewhat stupid.
You can find files with leading or trailing blanks (in ARTIST) with the following filter:
"$if($eql($len(%artist%),$len($trim(%artist%))),1,0)" IS "0"
You can get rid of these blanks with an action of the type
"Format tag field"
and the format string
$trim(%artist%)
All right, no offense, but I just thought there is no reason for those spaces and they can easily mess things up. But, hey, if there's an action for that, I'm good.
Trim will remove any leading or trailing blank spaces from a string. So if the string was " Text", then Trim would delete those spaces for you, leaving just "Text".