Courses not getting graded correctly

I have created a test course. The Minimum Grade Required to pass the course (set on the Course Setup page) is 50%. So I expect if they answer more than 50% of the questions correctly, the course will be marked complete, and they will get a certificate.

There are 3 single-choice questions. If they answer two correctly and one incorrectly, I expect the grade to be 67% and the course to be marked complete and the certificate to be issued.

What happens is the progress is marked 75%, there is no grade, the course is not complete and no certificate is available.

If I make the Minimum Grade for the question 0%, the progress is 100% (correct), the grade is 67% (correct), the certificate is available (correct), but the question is marked as 'Pass', when it should be 'Fail'.

How do I correct this behavior?