SHIP_TYPE_ID not copied from PO by Voucher Build

Hi,

We are using voucher excel upload to create PO vouchers and found that Voucher Build not copying the SHIP_TYPE_ID from PO (PO_LINE_SHIP table) onto the Voucher. It always takes the default from AP BU setup. We found from the voucher build trace that, the voucher build process actually blanks out the the Ship_Via_Cd initially and at later steps it gets it from BU setup. (i.e. SHIPTO_ID value gets copied from PO_LINE_SHIP table correctly).  So, we are not sure why is it doing for this SHIP_TYPE_ID field. I couldn't find any fix for Voucher build for this issue.