Weird sort order when search topics/posts with "in:first" and "order:latest" combination

I think it’s because you search in:first. The post you get as a result is not 19h old, it seems to be from 2017.
But I understand your problem. If searching in:first there is no difference between sort by latest post and sort by latest topic.
Is an example here at meta.
The result shown last (Configuring Facebook login for Discourse) has newer latest posts than the first result