Project Costing for contingent worker timecard with PO integration, PO in different currency than pr

Client is on 12.1.3. In Projects the Contingent worker timecard is integrated with Purchasing. We have a PO in a USD ledger but some conitngent workers have an AUD cost rate (in the PO). When the PO is entered you define the exchange rate type (Corporate), the exchange rate date (and resulting the exchange rate) so the commitment can be established. The PO was created using the exchange rate date in 2013.

The contingent worker submits the timecard in August 2014.  In Projects his August 2014 timecard is now costed using the exchange rate type AND EXCHANGE RATE DATE of 2013! Should this timecard not be costed using the current PA date (i.e. August 2014)?