Page # button is missing at top of thread for next to last page

[LookinAround]

This one is minor but curious. It happens in both FF and IE. Note in image at end of post the last page of the thread is 17. Yet page 16 button is missing. This is also true when I select 14, 15 or 17 page 16 doesn't appear.

Plus I just noticed this also happens in to a long thread in this forum as well! The last page is #22 yet page 21 button doesn't appear at the top of thread

p.s. Another problem! In FF, I uploaded the file Page16.jpg and clicked Thumbnail then Preview. Then I get this error

TechSpot Forums - Error
You do not have permission to view this page or perform this action.

Here;s the full image of the image I tried to thumbnail. (And note page #16 is missing from the list)