AP and PO Write-off process doesn't true up quantity delivered and billed upon successful completion

Hello

Many times, we have small accrual balances left on the POs and we use AP and PO Write-off process to write them off. Recently, we have noted that the process doesn't balance the quantity delivered and billed. E.g. quantity delivered = 1438 and quantity billed = 1437.73, so I have 0.27 over receipt ( Accrual). I use the AP and PO write-off process to write-off 0.27. All is good, the balance is cleared in GL and from the Accrual recon report. Now, I review the PO distribution, it still shows  quantity delivered = 1438 and quantity billed = 1437.73, where