Reach reports incorrect quiz answer as 100% instead of a percentage of total responses?

We have a quiz in which Reach reports that Question 1 had 45 responses. Of that 45:

• 24 users entered the correct answer, which is 53%. 
• 4 users entered a variation of the correct answer, which is 9%. 
• 6 users entered an incorrect answer, which is 13%, but Reach reports it as 100%.

In fact, all incorrect answers are showing 100%. Why? I can make the calculation manually, but why doesn't Reach make that calculation?

I searched the forums and documentation for an answer, but didn't find anything.

Thank you. -Eric