Scrollbar in pages tab of navigation pane

the last page(s) of the pdf file can not be reached by scrolling down the scrollbar.
They are out of scope of the navigatioin pane.

The problem arises if the last line of pages is not filled up with the maximum number of pages.
For instance:
I have a pdf with 70 pages.
I can scroll down to page 70, if I have 1 page in a row of the pages tab.
I can scroll down to page 70, if I have 2 pages in a row of the pages tab.
I can only scroll down to page 69 with 3 pages in a row.
and to page 68 with 4 pages in a row.

So this seems to be a math problem. Division with remainder.
If you want to see all the pages in the pages tab you have to adjust the number of pages in a row, so that no remainder is left if you divide the number of pages with the number of pages in the row.
This feature is also seen it Adobe Reader.

Any suggestions appreciated.
Can anybody confirm this behavior?

Thanks in advance.

„There are two ways to try to make a software system reliable: make it so simple that it obviously has no bugs, or make it so complicated that it has no obvious bugs”
Alex Martelli