Switch role to student, take quiz, can't delete attempt

When a teacher uses the "Switch role to" drop down, switches to student, and previews a quiz, the attempt is recorded, but cannot be deleted.

The teacher can no longer edit the quiz after switching their role back to teacher. The attempt cannot be deleted.

This can be seen on demo.moodle.org running Moodle Version 1.9.1+ (Build: 20080602)