I created a 26 question quiz and took it three times with actual scores of 9, 19 and 26. This is accurately displayed on the test results page for each time I took the test. But if I go to the reports page the scores are reported as 10, 20 and 26. If I look at the scores database field it has scores of 10,20 and 26.

When the database entry is incorrect, it appears to always be incremented by one.