Create a quiz with various types of question, including an essay. Make a couple of attempts as a student. As teacher/admin, review a student's attempt. Click a Make comment or override grade link. Type in a comment, and enter a grade that is out-of-range. Click save. The page should be re-displayed with a validation error. Verify that your commend has not been lost. Edit the grade to be in range, then save again. Verify the comment and grade is saved. Repeat the previous few points using Results -> Manual grading pages, rather than the starting from the attempt review page.