Steps to reproduce:

1. Create a course.
2. Enrol 1 user as students.
3. Create an assignment and, in "Grade -> Grade", set "Type" to "point" and "Maximum grade" to 10.
4. Save changes.
5. Go to the course grades, click over the "Turn editing on" button (to enable quick grading).
6. Set grade for student 1 to 50
7. Check the grade is set to 10 (instead of 50), because it's the maximum allowed.
8. Turn editing off
9. Access to the "Single view" tab and select the assignment.
10. Mark the "Override" column as checked, set the grade for student 1 to 50 and save.
11. Check the grade is not saved.

The expected behaviour should be consistent in both scenarios (when saving a grade from the Grader report and when overriding from Single view).