Functionality is applied when you are reporting picking with differences and the quantity of the picked parts is greater than the revised quantity, i.e., the quantity stated on the order line. In the dialog you will get a message informing you that the line has been over picked.
If the over picking isn't intended there are two ways to solve it depending on if shipment inventory is used or not:
Pick list line quantity must be reported with a greater quantity than the revised quantity.
Confirmed over picked order lines will report the quantity stated, an information message will be shown.