That s how it works for me. I click on thread I've looked at and it takes me to the first post I have not read.
If there is nothing that you have not already seen, it takes you to the beginning of the thread.
It "normally" works for me, but I've noticed if I haven't clicked on the alerts for a certain thread, then click on an alert, it will start me at the very beginning. Not a big deal, but now you have to scroll to the bottom to get to the advance button.