I just ran across this suggestion, but I have yet to try it out:
Copy and paste the whole document into notepad first, then copy the notepad text and paste that into your site. I think that should fix it.
posted by weapons-grade pandemonium at 11:54 AM on February 11, 2010
In other words, write your comment in a text document first, then copy and paste it into
the comment box. I have given up on using tildes, accents and cedillas in the comments because they always paste wrong. Unfortunately, I can't test this suggestion right now, because I would need to leave a comment with uncommon diacritics or punctuation, and then wait (possibly months) until I again run across the crypto on which I left the comment.