INV "Invalid transaction source segments" error

 We recently setup a 2nd Inventory Org to be able to place orders against from OM. I was able to place orders, book, pick release and ship confirm successfully. But it failed in Inventory transaction creation step, as a result the serial number still shows up as available. It got stuck in the inv interface table MTL_TRANSACTIONS_INTERFACE, with error "Invalid transaction source segments" . 

Found that the TRANSACTION_SOURCE_ID was missing in the interface table. On analysis, found that this field should be set to SALES_ORDER_ID from MTL_SALES_ORDERS table, in essence MTL_TRANSACTIONS_INTERFACE.TRANSACTION_SOURCE_ID  ==(should be set to) MTL_SALES_ORDERS.SALES_ORDER_ID. I see that a record was created in mtl_sales_orders table but the background process didn't copy the value over. After I updated from backend, it worked fine and created INV transaction.