Stock Valuation Report incorrectly reporting a value

With POP setting Update Stock Cost Price at Goods Invoice enter Purchase Order and receipt the goods in. Enter Sales Order, despatch and Invoice by mistake. Enter a Sales Return, receive and credit. Amend goods received on the Purchase order causes two entries in MovementBalance table to be left behind. One entry is for the Sales Return with a cost price and the amend goods received without. This results in the Stock Valuation giving a value of stock despite there being no actual stock.