Tax Rate Area Missing on OT Detail Lines

We are creating transfer orders between business units that are in different countries so VAT needs to be recorded when creating the voucher for the OT receipt.  Unfortunately, the VAT rate is populated in the purchase order header but is not getting populated on all of the detail lines even though the taxable flag is set to "Y".  As a result, the users are having to manually add tax when creating the voucher and is easy to overlook.  Is there a way to ensure this field gets populated when the OT is created or is there a batch job that