Update "Actual Cost" from CM?

When CM & P6 projects are linked, For each contract you can create or update the document as an activity.  I am able to create/update the p6 activity with Responsibility Code, Contracts and Expense Item that includes: Cost Account & Budget.  When I create and approve an Payment Req, the Actual cost isn't updated following another import to update the information.  What could be the cause of the non-update?  Any help is greatly appreciated.