Overriding Discount Payment Dates and the Remittance Advice in Nav 5.1

Hi Forum, has anyone come across this before. We have a user who when they do the Suggest Payments changes the Payment Discount Dates on the Applied Entries so they always get the discount. This is not so much of a problem but when they print the Remittance Advice it sometimes does agree with the amount to be paid and they end up over paying the Vendor. Also, they do not get the Discount on Credit Memos even though the Pay Terms are ticked to get discounts on credits. Has anyone else had this problem. Thanks Paul