It makes chasing back the context of an interaction difficult if not impossible.
What’s going on there? The system seems to get lost at times.
Maybe your interlocutor pushed the wrong button.
Be sure you respond to the post in question by hitting the top Reply, not the larger, general ‘Reply’ and then entering the ID of the poster you’re responding to in the text body.
Worked a long time in software development. This is a system flaw.
There have been times that I know I hit the correct REPLY but the system failed to record it. It’s inconsistent. The system should be made user friendly if not foolproof.
I did look at one of the five responses you had entered when I read your post above, and it started with ‘@’ and a username. From this, I deduced you had simply responded to the thread, and not the specific post. Was I mistaken in that? Because I’ve been here since the site opened, and I’ve never observed the behaviour you’re reporting.
I edited the post when I noticed and then added the user name it. The issue could be platform/browser dependent. Possibly a race condition.
I’m sure you mean ‘rare condition’ 
No race condition. It’s a computer thing. I can explain it to you if you like.
Do! I’ve never heard the terminology (and I’ve been a techwriter).
Posts failing to indicate which post it was in response to
Which posts?