Just noticed this today. I have looked at a small random sample of authors and it appears to be consistent.
If an author has between 11 and 19 stories, for example "Displaying stories 1 through 10 of 17" there is no button for page 2.
If I add &p=2 to the url, page 2 is displayed "Displaying stories 11 through 17 of 17" but there is no button for page 1,
20 stories has buttons for page 1 and page 2.
21 stories has buttons for page 1, 2 and 3.
Something simple I hope!