Whee, IE7, still haven't got it yet. :)
Anyway, nods, and a note, it's not only when you click on those two links, but when you come to the site period.
Say I do this: In the morning, I turn on my computer, and I have my browser homepage set to Elliquiy main forums page, and with permanent sign-in on. [I don't have it set as homepage of course! But just saying.]
So I turn it on, and Elliquiy pops up, but I wandered off for a bowl of milk and cereal in the meantime, takes me half an hour to eat. Then when I come back, I hit on the Show Unread Posts link.
This will be empty, or close to it, because you 'appeared' on the last 15 minutes active list, then disappeared again, and when you disappear all your Unread posts go poof. The code is probably done so that it takes your "last logon time", ie those 15 minutes when you appear and disappear for even 1 second, and shows you all the unread posts AFTER that time.
Even though you didn't actually do anything on the site that time.