When setting up categories and items, if you add grades then change aggregation from simple weighted mean of grades to weighted mean of grades and add weights, then change back to simple mean of grades, overall averages and course total no longer calculates correctly. The workaround is to change the aggregation to weighted mean of grades and remove the weights, then change it back to simple weight mean of grades to get it to calculate correctly again.

Steps to reproduce:

1) Enter Categories and items setup and add grade items (default calculation is Simple weighted mean of grades)
2) Add grades for users, then verify that the overall averages and course total are calculating correctly
2) Change the category calculation to Weighted mean of grades
3) Enter weights
4) Change back to Simple Weighted Mean of Grades
5) Calculation is now incorrect.