Why is PHP's SoapClient creating a different namespace for the header than the body?

Question

I'm trying to communicate with the eWay server and had everything working until we ended up needing to switch to a different API. The problem is that SoapClient is creating a different namespace for the header (that includes the authentication) then from the body, which, obviously, doesn't get me any results. Instead, I get eWay's servers saying it must have the authentication information.

Here's my code:

   $client = new SoapClient($url.'?WSDL', array('trace'=>TRUE));

   // Set our SOAP Headers for authentication
    $header_body = array(
        'eWAYCustomerID'    => $gateway['customer_id'],
        'Username'          => $gateway['username'],
        'Password'          => $gateway['password']
    );

    $header_var = new SoapVar($header_body, SOAP_ENC_OBJECT);       
    $header = new SOAPHeader('http://www.eway.com.au/gateway/managedpayment', 'eWAYHeader', $header_body);
    //$client->__setSoapHeaders($header);

    try {
        $response = $client->__soapCall($action, $xml, null, $header);
    } catch (SoapFault $e)
    {
        echo 'SOAP Fault: '. $e->getMessage()."<br>\n";
    }

As you can see, I've tried it with and without using a SoapVar for the header, all with no luck.

Here's the XML request that is being created:

<soap-env:envelope xmlns:soap-env="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ns1="https://www.eway.com.au/gateway/managedpayment" xmlns:ns2="http://www.eway.com.au/gateway/managedpayment"&gt;
<soap-env:header>
    <ns2:ewayheader>
        <ewaycustomerid>87654321</ewaycustomerid>
        <username>[email protected]</username>
        <password>test123</password>
    </ns2:ewayheader>
</soap-env:header>
<soap-env:body>
    <ns1:createcustomer>...</ns1:createcustomer>

Does anyone have any ideas here? I've been banging my head on the desk for far too long today.

Thanks.