Occasionally, but not always, after I have read all the “New” items - needs to be about a half dozen or more - I will see a 1 or a 2 next to “Unread”. When I click “Unread” to see what came in while I was reading “New”, there are no topics and all I get is the line saying so. Usually when I start reading “New” there is nothing shown on the “Unread” title and there is by the time I finish. Seems like a bug.
BTW: I usually move from one topic to the next in “New” by flicking the topic to the right using the touchpad to re-expose the topic list, wait for it to update, then click another topic. I don’t always take them in display order.
This is with Safari 7.0.1 on MacbookPro Retina 2012 with Mavericks.