As a teacher I see that some people accidentally grade 'acceptable' because that's the grade that is stated automatically. They forget to change the grade to the one that matches the feedback. Also there are sometimes troll-graders, who just grade stuff without reading, give feedback and send it in.
My idea is to put another option in the list, which will be selected automatically, in stead of the acceptable button: make your choice. And that option can't be submitted. So people won't forget to select a grade.
Customer support service by UserEcho