in the grading page there is alert before leaving the page about changes that not save will be lost, this alert should be shown if the user already saved the changes.

1. login as teacher
2. enter into assignment
3. click on grade button
4. if you click on the links in the upper left corner for return to course or to activity you will be able do it without any alert messages
5. enter again to grade page
6. now change the grade of give a feedbak
7. click on the "save changes" button
8. try to leave the page - you will get popup alert that any changes you made but not saved will be lost. this message unnecessary