Discount Cut Off Date in 9.1 R04570 Not Working Correctly

We have a vendor with payment terms of 1%10 / Net 30.  An invoice was entered with an invoice date of 4/30/18, which calculated a Due Date of 5/3/18.  The vendor was not paid until today, 5/14/18, and we set the Discount Cut Off date to 5/5/18, (after the Due Date) but the payment generated included the unearned discounts, even though the due date was 5/3/18 - which was the date at which a discount was earned.  We tried running R04570 with Discount Cut Off Date set at 4/26/18 and 5/3/18 as well, and in every instance the payment included unearned discounts.

Are we misunderstanding that discounts are based on the Invoice date, and that the Discount Cut Off date should be any date after the invoice Due Date in order to NOT take the discount when it isn't earned?  It doesn't seem to matter if you put the cut off before, on or after the due date, the system is still taking the discount.