Form Quiz does not alway show correct answer mark.

I have made a quiz and marked the correct answer:

Both questions 8 and 9 have the correct answer mark. 

But when I look at the response it looks like this: 

For number 8 the correct mark is missing. It is there for number 9. 

How can it be it is missing?
I have copied the quiz. It still appeared in the new one. And I have tried to delete it and set it again. It doesn't help.

Hope you can help. 

See you Søren