With AJAX on in the Grader report, after you enter a grade, when the page reloads, the Update button is hidden.

Replication steps:

1. Log in as admin/teacher
2. Navigate to a course that has some gradable activities
3. Navigate to Settings > Course admin > Grades
4. From the drop-down at the top of the page select Grader report
5. Navigate to Settings > Grade admin > My report preferences > Grader report
6. In the General section set Enable AJAX to Yes
7. Click Save changes - you should be returned to the Grader report
8. Enter a grade and click on Update - the page reloads without Update button
9. Click the configuration icon for the grade item
10. Check Locked or Clearing the Overridden status and click Save changes - the submit button reappear
11. Enter another grade and click on Update - the page reloads without Update button
12. Navigate back to the course then return to the Grader report - The Update button is still hidden

Turning off AJAX in Grader Report resolves the issue