@codinghorror, et whomever.
I’ve noticed that there has been confusion in various threads where people will reply to someone else, only to discover the their comment is suddenly directed at someone else. It turns out, the problem starts if you read a comment, and hit the “X Replies” button on the comment to see how people reacted to that post. You can then highlight someone else’s post in the replies listing and when you hit “quote reply” Discourse automatically credits the author of the original comment, not the replier you’re actually quoting, and turns it into a reply to the original commenter, instead of the replier.
I don’t know if this explanation of the issue makes sense, if so just ask questions if you’ve got 'em. But a perfect example is here in this reply to (I thought) @mindysan33, but it came out to @shaddack, since I was viewing @mindysan33’s reply to @shaddack through the Replies dialogue.