Yes - I posted a reply whilst on p11 (because that was where I had got to, and that was where the one I was quoting and replying to was).
And having clicked Post Reply, what I saw was the second screenshot above. Can't remember how the first one came about - I captured it earlier because it seemed that that behaviour might have caused me to miss a post which left someone hanging on for a reply.
As far as I recall, the old forum s/w would have positioned me at the end of the topic, not left me where I was but also showing the post I'd just made.
The problem is that if a topic is fairly active, and someone posts after having been away from it for a while but had left it open, they might well see what was the last page at the time they stepped out, but is no longer, but the behaviour will leave them still seeing that, with their post at the end.
The indications that there have been posts made while they were away are subtle, to say the least, and easily missed. With the old forum, being teleported to a page you'd never seen before was a much more obvious "notice" of that.
I don't know if the current behaviour is what it is, and we just have to lump it, or if it can be tailored....