Direct Credit Payment for 2 different customers

Hi there

I have a customer who pays by direct credit for 2 different customer accounts. This month, both customers have one $200 invoice each. The customer has paid one payment of $400, but when I do the 'create invoice payment' (doing 2 separate transactions, 1 for each customer), then go to the bank transactions to match the payments, there is nothing to match, just the original $400 payment waiting to be allocated. Meanwhile both customer accounts show that the invoices have been paid. Can someone please tell me what I am doing wrong, or how to allocate the payment?

Thanks :)