In 4.5.1+

1. Create an assignment with some students
2. Submit for one of the students
3. Go to Submissions page (/mod/assign/view.php?id=NNNNNN&action=grading)
4. Select filter to Requires grading
5. Select Grade button beside the filter settings to go to the grading page (mod/assign/view.php?id=NNNNNN&action=grader&userid=NNNN)
6. The grading page shows No user selected

This could maybe be linked to https://tracker.moodle.org/browse/MDL-84332