CoursePress Pro Bug: Grades not calculating the percentage correctly

I am not sure exactly why the grades are not calculating correctly for me. I have a multiple choice answer with 13 responses. All 13 responses are correct. The minimum score to continue is 80%.

I understand that the score is rounding up and down based on the decimal, but the issue that I am having is that the numbers are off by several percentage points.

i.e
1 correct answer yields a score of 8%
2 correct answers yields a score of 15%
3 correct answers yields a score of 23%
4 correct answers yields a score of 31%
5 correct answers yields a score of 38%
6 correct answers yields a score of 46%
7 correct answers yields a score of 54%
8 correct answers yields a score of 62%
9 correct answers yields a score of 69%
10 correct answers yields a score of 77%

then it breaks and gives the following

11 correct answers yields a score of 77%
12 correct answers yields a score of 85%
13 correct answers yields a score of 92%

Thoughts?