I have noticed that some posts in this forum are marked as replies to other posts. Here's one example. If you look at the top right corner of the post there is a little reply arrow and a picture of the avatar of the person who is being replied to.
Also, when I write a post that I intend to be a reply to someone else, I can see the person's avatar at the top of the editor pop-up (and I can click the reply icon to choose how to respond, which is a neat feature).
But the actual post is unmarked. For all I can tell it looks the same as a reply to the topic.
Doubly confusing, if I edit this post again I can still see the avatar at the top, so Discourse is clearly keeping track of the post I replied to, just... choosing not to display it. Why not?
I find this very annoying and have been wondering about it for months.