I have seven integer fields from my table represented in a business object.  One custom property adds the values and returns the total (int).  A second custom property determines the percentage (total points / total available) -- called rating.  A third custom property references the percentage and presents a letter grade (A, B, C, or D).  Rather simple.  If I click new on the form, the defaults work fine (all int fields maxed at 10, total points is 70, the rating is 100% and the grade is 'A').  The moment I change a value in any one of the seven integer fields, the total points and the rating are zeroed out.  The grade always reverts to the lowest possible choice.  What are the possible reasons that my custom fields are not updating properly?

Thanks!
Bill