I have had the same thing happen to me too often to blame it on being tired. I think there's a glitch with the website related to unread topics. Besides taking me to the end of the Next unread topic now and then instead of taking me to the first unread post in the next topic, the website seems to hide some posts on me now and then, too. Here's an example of an experience I had. I walked away from the computer once for an hour after reading all the current threads only to come back and find one new post along with a bunch of older posts that were 2-4 hours old. I didn't see the older posts because they weren't there an hour earlier, but the time stamp on the posts said they had been there for 2-4 hours. If it had only happened once to me I'd question myself, and I did, but after it happened a few times I started watching for missed posts and I have been finding them. I wonder if that's what's happened to you.