Question: More people with the same issue?
I regularly use the "Show unread posts since last visit." I notice that i get more pages than actually exists. So the 4th page are really the same items like page 3.
This maybe sometimes applies when there is only one thread listed on page 4 and you already read one post on page 1, 2 or 3. Then selecting page 4 may cause that page 4 doesnt exist and you will see page 3 with (nearly) same content... Thats what I sometimes see...
That sounds plausible! It is subtracting the currently read items. Will verify the next time.