The pagination seems to be screwed up in threads sometimes. I've noticed it in a couple of threads, but specifically in the "C book recommendations" sticky.
Here's what I mean,
"One" is the page 8, however if you click page 9, you're taken straight back to page 8. Even the tooltip is wrong :)
I couldn't find anything about the bug on the interzweb, maybe I didn't look hard enough. Probably fixed in vBulletin Version 4.0 but who knows.
"Tooltip for page 9", Tooltip says "Show results 121 to 121 of 121" -- makes sense ;)
"Click page 9" -- takes you back to page 8.
At least you can still change the 8 to a 9 in the address bar.
I've seen this on other forums. My guess is that it is because some posts have been moved or deleted and so one part of the code thinks there are more posts than there actually are.