The first graded record is always by lastname A-Z.  However, the filter uses the user preference sort from the View All Submissions page.  This has caused major issues because it seems that the default sort on the gradingtable is by userid.  I would propose to have a default sort that is changeable and set to lastname by default and have the grader interface always show the 1st user as shown in the filter unless a specific student's grade button was selected.

To recreate the issue:

1. Go to an assignment in a course with some students in it.
2. Go to the View all submissions.
3. Set the sort to be by lastname A-Z. Take note of who the first student is.
4. Change the sort to some other sort method. Take note of who the first student is (to see this issue easily, make sure it is a different student)
5. Go back to the main assignment page and click Grade.

You will see the submission grading page of the student who was 1st in the lastname A-Z sort. But if you look at the filters area, you will not be looking at the 1st student record. The filters sort will be in the saved sort method.  You might be looking at student 9 out of 40.