For some reason, I've noticed this recently as well - and solved it by hitting F5 (on internet explorer) or clicking the Refresh button.

Usually, on forum systems, the posts are not cached - however, for some reason, on this one, it seems to cache them (save a copy and use that copy until you refresh it, or until the copy it has 'expires').

It only happens occasionally for me, but when I logon and notice that the last post was 3 hours ago (I know FT better than that ) I hit refresh - and poof - more posts to read.