Quiz with shuffled questions: manual grading pop-up shows the question number students saw during the attempt

Steps to reproduce:

1. Create a quiz with question order: randomly shuffled.
2. Add several essay questions.
3. Attempt the quiz as several students.
4. As teacher, go to Quiz administration -> Results -> Grades
5. Click one of the Requires grading links.

Actual result:

• The main results table has column headings Q1, Q2, ... as on the edit quiz page. (Note, these are consecutive numbers, not slot numbers.)
• The grading pop-up shows the question number the student saw during the attempt (which is different for each student).

Expected result:

• ???

Moodle version is 3.0.2+ build 20160225.

(Updated by Tim Hunt based on the comments below.)