Link to "New Post" opens an old post

I've had this problem for about 2 months and have not found a solution despite searching on Google and inside these forums. So I apologize in advance if the issue has already been discussed somewhere else.

I'll explain the issue with an example.

Let's say that 10 people post replies to this very message before I go into Standby. I'll receive the usual "notification email" warning me about the first new reply (at this stage that's, post #2). If I click on the "...new-post.htm" link in the email, my browser of choice (Firefox 8) will accurately open the thread at the first of the 10 new replies, ie, post #2. No surprises so far. I'll read that post then the other 9 new posts.

So now the thread has a total of 11 posts and I've read all 11.

If, after reading all those messages, I decide to walk away from the computer, and, let's say, 3 new replies are posted, then things will start behaving strangely. Once I get back to the machine, I'll see that I received a second "email notification" pointing to the first new post since I went away (at this stage, that's post #12). By clicking on the link inside the email, however, the browser will load the thread at post #2 again, which was a new post at some point that day, but it's just old news by now. If, then I get 20 new replies, then click on the link inside the "email notification" (or even the arrow on the "User CP") this thread will still open on post #2, which was new at one point, but no longer is.

This problem also happens in IE9! The only way to get the forum to recognize that I have already read all the old posts and open the thread at the truly new message is to log-off, close the browser and re-open it.

I hope my explanation wasn't too daunting and that there's a solution for that. When I used to use Firefox 3.x, there was no such problem. Maybe the issue is related to some setting on both IE and FF...