Invoice Register - Single invoice for multiple receipts

I'm using the invoice register & invoice approval screens to capture and match vendor invoices to multiple PO's.

When i'm in the invoice approval screen, i FIND VOUCHER and then click Functions --> Purchase Order. 

In the PO field, i select multiple PO's to match the invoice against. 

When i do this, the system creates multiple invoices (per PO)..

Is there a grouping option that I am missing?