Some more info about the post I cannot edit. If I edit @username even to delete one character and put it back (so it still reads correctly), it won't tag when saved. If I delete the @ and type it back in, it won't tag when saved. If I delete the last character of the username, then pick the correct name from the autosuggest box, it won't tag. But, if I start a new line and enter @username from scratch, it WILL tag when saved. And, if I highlight all of his post and click "remove formatting" on the toolbar, even though no formatting appears to be in the message, ALL of the broken tags suddenly work!!