I've been using mp3tag for years to organise my mp3 files and I trust it implicitly.
I was pleasantly surprised when I discovered that mp3tag could also handle tagging in my m4a files.
Unfortunately I did not notice that it was silently truncating my comment tags.
This is very disappointing, as I was not using mp3tag (2.58) to make any changes to the comment tag.
I understand that strictly speaking, I should not have been allowed to insert >256 character comments into the files in the first place (via winamp), as this is not the apple standard.
This is harsh as I feel this is more an application limit than a file format limit, as itunes truncates the displayed comment text to 256 chars for all file formats, as I remember.
Anyway, I see why mp3tag is obliged to uphold this arbitrary limit, but I think it would have been polite and professional for mp3tag to warn me that it was about to remove information from the files.