Is Price Change on GR caused by Standard price valid for one month?

We made a goods receipt with document date April 30 and posting date April 30 on May 3rd, SAP made two FI documents, one to April to the Inventory account and GR/IR, then in MAY 1 there is a price change document posted to inventory and price change account. There is a new standard price for the part which is valid for one month. Is that causing the price change if so how to reverse so that Price change posting does not happen?