It might be not so much an error as much as it's simply a mismatch. I could probably give a more specific conclusion if I was pointed out a few specific instances of it happening in posts, and not just what markings seem to be mismatched and/or undefined. (I know one person who occasionally has markings in his posts that do not confuse my computers or browsers, but *do* have codes that end up being unmapped on the server I use to backing up posts in case of a disaster, for instance ... something which I can't really do much about, as it is not my server to tamper with.) As well as their system's/browsers' encoding settings (for instance, my default is UTF-8 pretty much everywhere).