XF 1.5 Opening thread seeing first post, opening thread seeing last post

[XYZ500]

I'm not quite sure how to structure the question. On the forums, there are some threads which I open and I am taken straight to the last post and it shows up on my screen. There are some threads which I open and I see the first post. Why is that? What is the difference between these threads?

 

[Paul B]

Why is that? What is the difference between these threads?

It depends whether you have read it or not.

For threads with unread posts, the first unread post will load.

For threads with no unread posts, the first post will load.