I've read about it there: Anzeige der Tag-Größe (%_tag_size%)
According to this, mp3-files with existing tags that should be preserved need to be rewritten as a whole to remove the padding/unnecessary space.
Yet my described behaviour only relates to 'cleared' mp3-files without any tag-data included, so the tag-container will be created and written 'from scratch'. If 'padding' would be the cause, why not avoid it for the initial tag-creation process (as far as possible)?
Thus is it feasible to tell the program to create the ID3v2.3-tag with only the string-data from the first filled tag-field and add every other remaining tag-data afterwards?