Subtotal and Discount Amount data copy not working on "add"

We are switching methodologies with our estimates. I am trying to implement a subtotal and discount record behavior where the amount is copied to a custom transaction column field.

The code seems to be simple to implement but it only works on edit, not on add.

Item -2 = subtotal item
Item 5476 = discount item

I have the associated form functions assigned as these methods are named. The code is being called with no problems but after clicking the add button the custom amount field is not updated with the correct amount. The subtotal has a different behavior, it will put 0.00 in the custom field whereas discount will put the entered (not calculated) amount. So for example enter a 10% discount and it adds 10.00 to the custom field, not the applicable calculated 10% of the subtotal.