Unread Posts and New button

[#1]

I have found that when I use the Unread Posts listing and then the New Button, it doesn't always take me to the last posting I had read.
Could it be that that when I have read all the ones I am interested in I push the mark all posting as read, it goes away and marks those that I havn't read but also those that have come in since I last refreshed the last and not those that are still visible to me.
Or is there a genuine fault in the Jump? 

[#2]

When you click Mark all as read it does mark everything read including newer posts not in the displayed list.
I first click Unread Posts again to check for anything newer and then quickly (if there is nothing I'm interested in) I click Mark all as read to keep the window for new posts to sneak in as small as possible.