The First name and Surname initial letters filter disappears when Assignments per page is set to show as many or more students that is in the gradebook. This is confusing for the graders.

Steps to replicate:

1. Add a number of students exceeding 10 (11 is enough) to the course
2. Add an Assignment
3. Go to View/Grade all submissions
4. Set Assignments per page to "10"
5. The First name and Surname letter filtering is available
6. Set Set Assignments per page to "20"
7. The First name and Surname initial letter filtering is no longer available