OE invoices not showing prepayments

If I enter an order in OE and enter a prepayment and post the order, when I later invoice the order the prepayment is not shown against the invoice, but only on the right hand side of the invoice totals as an order prepayment.  If I enter the prepayment and ship and invoice the order all before posting, the prepayment shows correctly against the invoice.  How can I get prepayment entered before the order is complete and invoiced to show up correctly?