[whpalmer4]

It is implementing the conservative approach. A part of something can't very well be due after the whole! Now, when you move the due date of the child beyond the due date of the parent, it could throw up some sort of warning that you are making a change which will be effectively ignored; alternatively, I could see making a case for adjusting the parent's due date to match the child, if a warning is given and confirmation obtained. But I don't think you want to sort by the due date if it isn't the due date that will be enforced, and I don't think it is okay to blindly adjust the parent's due date to match the child's.