Cost variance at Voucher Match

Hi all,

Could anyone help me with the following issue:

For item X (line type S; purchase price level 2; in Line Type Constants, for line type S, the Voucher Match Variance Account is checked), the Purchasing Costing Method was initially setup at 06. Transactions were entered using this item (orders, receipts, inventory issues, vouchers). The Purchasing Costing Method for this item was then changed to 01. A receipt was entered for 10 units of item X, with the total cost of 2822,60. An inventory issue was then entered for the 10 units. Afterwards, at voucher match, the amount to voucher was modified from 2822,60 to 3000 (the quantity invoiced remained the same as the one received).