If you have a forum for example which has ratings with a scale for example the "useful" one here :http://qa.moodle.net/mod/forum/view.php?id=251 it is not possible to manually edit the ratings via single view because when you click "update" they just return to "No grade". Changing them via the Grader report does work however, as does single view when you modify points in assignments. I don't know if it's the difference between having a field to type a number in and having a dropdown - because I note that in single view with a scale as a grade the Feedback box does actually save, even though the rating from the dropdown does not.