Anyone having issues with Payables deducting the Freight Amount from the Discountable Amount during

Since upgrading to 12.1.3 two years ago, we have been having an issue with discounts in Payables.  If there is a line entered as Freight on the invoice, during the validation process, Oracle deducts the Freight amount from the Discountable amount and takes the discount on the lower amount.  For example, if I have an invoice for $200.00 with a $10.00 freight charge, the invoice total is $210.  When the invoice is first entered, the Discountable Amount shows $200.00, which is correct.  After the invoice has been Validated, the Discountable amount now shows as $190.00.  Oracle Support has not been