LCM in Average Cost Org - Actual Landed Costs continue to be updated

Hi -

We are using LCM in Average Costing Organization.  After PO is received and invoiced, we have a scheduled request set that runs to run Matches Interface Import and Submit Pending Shipments requests.  We have a PO received on April 20 and invoice matched on April 23.  The Landed Costs for this received PO continue to get updated; the last update was on June 20.  Is this expected in an average costed organization?  We were under assumption that landed costs would be 'frozen' once the invoice was matched and Submit Pending Shipments was completed for this PO.

Thanks