If a correction is made to a confirmed purchase order and that change results in a decrease to the original budget reservation ...

If a correction is made to a confirmed purchase order and that change results in a decrease to the original budget reservation related to the purchase order amounts/accounts; then you can choose to include or exclude the amounts for the corrected purchase order, until the purchase order is confirmed, if it results in a reduction to the reservation.  This option is here to prevent a reduction in budget reservation due to a purchase order correction until the correction is confirmed, since a correction may be reverted.