When the system cancels an invoice/credit memo, it simply tries to reverse the postings. However, this is not always possible. For example, if an invoice is canceled in which a material is debited, the postings can only be reversed if there is sufficient stock of the material when you cancel the invoice. If there is not sufficient material stock, the reverse posting is proportionally distributed; the amount covered by the stock is posted to the stock account, the remaining amount to the price difference account.

When you cancel an invoice/credit memo that refers to a purchase order, it is not possible to exactly reverse the original account postings if another invoice was subsequently posted with a different price.