@Jam can't replicate it... using master
Bug in post order (v1.17.0)
I have a strange behaviour on a topic created by one of my users. He started the topic, then added replies (it's a topic where he presents his work by making a kind of summary in his first post). But, it turns out that the posts are not in the right order. The ids don't follow each other ... post 1742, followed by 1744, followed by 1731 ... and indeed, the post timestamp confirms the wrong posting order.
Strange, isn't it?
Maybe the "Sort by votes" was activated in topics?