Quick Grading in Assignment module does not turn on in some circumstances

With the new Assignment module there is no obvious way to turn on Quick Grading when looking at a list of students to be graded.

When looking at a list of students to be graded, there is a "Quick grading" item with a check box at the bottom of the list of students (see attachment). Clicking on this check box would seem to be the obvious way to turn on Quick grading, but nothing happens.

In order to turn on Quick grading a teacher has to:
1) check the Quick grading check box
2) then, select a number in the "Assignments per page" drop down menu - only then will Quick Grading be possible.

To turn off Quick Grading, the reverse is necessary.

This is very opaque and not intuitive.

Solution:
either activate Quick Grading a soon as the check box is elected, or have a [save setting] button to the right of the Quick Grading check box