Steps to replicate:

1. Create a course.
2. Create an assignment activity.
3. Enroll two students.
4. Navigate to Site administration > Grades > Grade category settings and select Weighted mean of grades in Available aggregation types setting.
5. Navigate to the assignment activity grading page and give a grade to both students.
6. Navigate to Gradebook setup page.
7. Edit a course category and set Aggregation to Weighted mean of grades.
8. Navigate to Single view tab, choose one student and override course total grade.
9. Grader report will look like:
10. 
11. Navigate to Gradebook setup page.
12. Edit a course category, set Rescale overridden grades to Yes and double Maximum grade.
13. After this change grader report will look like:
14. 
15. All grades for course total were marked as overridden. Therefore, if the grade is changed from the activity the course total remains the unchanged.