Problem with .NET web service accepting an xmlnode as a webmethod parameter

Question

I have a web service (asmx) web method defined like this :

[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
[System.ComponentModel.ToolboxItem(false)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
// [System.Web.Script.Services.ScriptService]
public class CisalWebServ : System.Web.Services.WebService
{

    [WebMethod]
    public string HelloWorld(string secretkey, XmlNode terajob)
    {
        return "pending...";
    }
}

When I send the request via postman this is the xml that I'm sending..

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <HelloWorld xmlns="http://tempuri.org/">
      <passcode>mypasscode</passcode>
      <terajob> 
      <teraId>1</teraId>
      <kustama>2</kustama>
      <soyani>job2</soyani> 
      </terajob>
    </HelloWorld>
  </soap:Body>
</soap:Envelope>

However, when I check the XmlNode teraJob's innerXML .. it only shows one element (teraId). I was expecting it to show all the element's inside of 'terajob'

Is this not the case?

If i change the xml to :

 <?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <HelloWorld xmlns="http://tempuri.org/">
      <passcode>mypasscode</passcode>
      <terajob> 
      <terajob>
      <teraId>1</teraId>
      <kustama>2</kustama>
      <soyani>job2</soyani> 
      </terajob>
      </terajob>
    </HelloWorld>
  </soap:Body>
</soap:Envelope>

I get all three elements.

<teraId>,<kustama> and <soyani>

Why is this? Why do i have to add the xml element terajob twice?