The main 'new posts' button at the top (for all forum topics/posts) works fine for me, but within a topic the '4 new posts' link often doesn't work - as letsgetem says it often takes you back to a post made some time ago, rather than just to posts made since your last visit to that topic.

Something to do with the cookie being updated when you visit a particular topic, rather than just when you visit the forum ?

Edit: just did a few trials & only got the true new posts each time ie working as it should.