On some (but not all) Essay Questions, after grading all students, the Quiz Statistics will report that 100% of students got the item correct. However, when I go into SpeedGrader, I can see that 4/20 students got it correct, so Quiz Statistics should show 20% correct, 80% incorrect. [Exporting a Student Analysis also shows that only 4 students answered correctly.] Why is this happening? How do I fix it - or prevent it from happening on other Essay Questions?