Double cost booked in Project Costing from Timecard and from Vendor Invoice

Hi,

We have a scenario where user wants to book timesheet cost from third party application in Project costing against the project. So the cost is accumulated in PC. But user also receives a PO based Vendor invoice for the same cost from AP and is interfaced to PA. Now we have double cost booked in PA.

How can we nullify this double cost ? We have a requirement to reconcile the timesheet entered and approved in timecard application which gets interfaced to PA with the Vendor invoice received from the Supplier.

Any suggestion how can we do this?

Also Is this a normal scenario where in OTL timecards are received in PA along with Supplier invoice ? Isn't there something incorrect?