It looks like the numbering function starts updating the top page-number buttons only on page “6” and thereafter. From page “2” through “5”, the button sequence remains 1 through 4. There is no way to use them to go to page “5” when on page “4”, nor to go to page “6” when on page “5”:

It’s probably a good idea to double check the logic and math for all min/max limits (I once received an empty/error page somewhere when inadvertently hitting the max-end button).

BTW, as a suggestion for design symmetry, both end “bracket” buttons should display the visual-cue “PAGE ###”.