If we are working with more no. of pages in the Page Builder and the name of the pages are longer in text then few of the pages goes outside the display window. if we use the Shift Range of Pages Forward/Next Range of Pages tool then it should come in the display range (last pages can be displayed & initial pages gets hide). But it does not happens.
Check if this is a bug or sometime else. I think in the earlier version this problem was not there.