Approval allowed when invoice has a distribution variance

Good morning.  We have certain situations where an invoice which has a variance between a line amount and the sum of the distribution lines is getting approved.  After the invoice goes through validation , a distribution hold is placed on the invoice so it cannot be paid.  However, we expect to receive an error message at the time the user clicks the 'Save and Return to Notification' button.  Is the logic which checks for this variance in the approval workflow seeded logic? 

Below are examples where the error message is recieved as expected and where it is not reeceived, allowing the invoice to be approved.