grade report fails to save after edit with multiple tabs

Test setup

1. Create a course
2. Enrol 3 users, "A", "B" and "C".
3. Create 2 groups, "Group 1" and "Group 2".
4. Add user A and B to group 1;
5. Add user C to group 2.
6. Edit the course
   1. Set the group mode to "visible groups".
7. Go to gradebook setup and add a grade item with default settings.

Test navigation

1. Navigate to the gradebook of the course you created
2. Navigate to the User report
3. Select Group 1
4. Select User A
5. Open a new browser tab and navigate to the same page as the initial tab (Note: in some browsers you can do this by right-clicking on the tab, and choosing "Duplicate tab")
6. Select Group 2 in the new tab
7. Select User C
8. Return to the initial tab and select User B.
   1. Confirm: User report for User B should be displayed (rather than an error reporting that the user is not a member of this group).

Navigation test can be repeated for reports other than user report.

Test Grading

1. Navigate to the gradebook of the course you created
2. Navigate to the Grader report
3. Turn editing on.
4. Select Group 1.
5. Open a new tab and navigate to the same page as in the initial tab.
6. Select Group 2 in the new tab.
7. Return to the initial tab
8. Edit the grade item for User A.
9. Save changes
   1. Confirm: Changes should be saved successfully and updated grades displayed for Group 1.