Quiz overall feedback incorrect as based on rounded result

1. Create a quiz with 15 questions
2. Set the overall feedback to display "You passed!" for 70% => 100% and "Try again" for 0% => 70%
3. Attempt the quiz and get 10 questions right (i.e. 66.7%)
4. View any of the feedback reports

Expected result:
"Try again" is displayed (as student did not reach the 70% pass mark)

Actual result:
"You passed!" is displayed

The problem seems to be that 'quiz_report_feedback_for_grade' is called using the output of 'quiz_rescale_grade'. However, the third parameter is left as the default 'true', so the grade is rounded to 7 (out of 10), before it is returned.