Unable to select CPA while creating PO from requisition tab

A user is unable to select a Contract Purchasing Agreement no while creating a purchase order in the Requisition tab under Purchasing Buyer's Work Center.

Is this an intended functionality or a bug.

Currently the buyer has to open individual PO lines and assign CPA no. as a souce document. It is very labour intensive if the user has to select scores of line and assign the CPA no. to individual line.

Another option of asking end user to select CPA no. while raising the requisition cannot work for us as most of the end users are not always aware of the existing contract with the supplier.