When you generate a new collection or payment remittance, all invoices appear to you by default, even those that have already been the subject of a remittance. For now, the only way to know if there are any invoices that have already been sent is through the blue bar in the rightmost column. The problem is that if that bill has not yet been paid or collected, but has been remitted, it does not have any marks to detect it as a remittance.