That MP3Tag on Windows seems to preserve all frames in tags fine. The only thing I noticed with a quick try is that it doesn't recognize if there are multiple V2 tags in a file, so RNOTags is better for cleaning your messy files ;)

I also tried MP3TagEditor again and it really loses lots of data from files. Pretty much every file lost some information from its existing tag, some even half or so. It also didn't succeed to read some tags at all, so all fields were empty even though there was a tag with information that should have been shown. This might be an issue with the id3tag.library and affect all programs using it. The program also writes a comment frame always, even though there isn't a comment... and hitted in the log immediately, so no thanks and this is why I wrote my own program :)