Hi Judson,
Thanks for sharing this answer, i am also facing the same issue. But here in my case i have extension field in Items nodes and also got the xml node from customer invoice xml, like below but when i process the xml it adds invoice request but dont maps th "test" nodes data to that extended column.
<n1:test_0LIGMSME2T388H1SZMFGTNHGN_Y38WD8BTY xmlns:n1="http://0008768412-one-off.sap.com/Y38WD8BTY_">test data</n1:test_0LIGMSME2T388H1SZMFGTNHGN_Y38WD8BTY>
Could you please suggest what i am missing.