Faulty links to "first new post"

[Goldgar]

In certain threads, I find that clicking on the link to the "first new post" doesn't actually take me to the first unread post, but instead to a page several pages before the page containing that post. An example is the "Word Association" thread in the Water Cooler/Game Threads forum. The same thing happens if I click the "Last Post" link.

Now, that's a thread with a huge number of posts, so maybe it's just some limitation of the software. Is this what I should expect, or is something gummed up? I've repeatedly marked all posts as read, but it doesn't have any effect on this behavior. I have to click the "Last Page" link to go to the last page, and scroll down from there to the actual new posts.

It's not just this thread, but I can't remember which other thread had this problem -- as I recall, it was another loooong thread. Is it just me, or is it a software limit, or what?

[Go? Fencing?]

It also happens in the Question Game and the Cocktail Party.

[scrapinpeg]

It happens to me in threads that are several pages long. If I click on most recent post, it sends me to a page several pages back. Ditto for when I post a reply in one of those threads and get sent back to the thread. Ditto for when I click on a rep link (which is confusing because now I can't tell what I got repped for).

Any ideas why this is happening?