Wrong Line PO getting passed from WFR

Dear,

The wrong Line PO getting passed when verifying the batch/document in WFR with blank line PO.

As per design when Line PO is blank then the Line PO should passed as Header PO. But in some cases, when we modify/change the Header PO then the line PO is getting passed as old Header PO and not passing the new/changed header PO. And due to this reason, the batch gets errored out at SOA level either with "Mismatch Currency" or "ERS PO" error.

I need help to make this correction to ensure that whenever Header PO changed and line PO is blank, then the Line PO should passed as Header PO.