.net generate proxy classes problem (wsdl/svchost) by soapHeader

Question

I'm using a web service from .Net C# client application. My web service has a method which return generic list and in my client application I use Configuration Service Reference to change array to generic list.Its working correctly. But when I add a soapHeader to my web service Configuration Service Reference to change array to generic list its not working and return Array instead of generic list.

---

public class Service1 : System.Web.Services.WebService 
{
    public Authentication authentication = new Authentication();

    [SoapHeader("authentication")]
    [WebMethod]
    public List<string> HelloWorld()
    {
        List<string> result = new List<string>();
        result.Add("oguzhan");

        return result;
    }
} 

public class Authentication : SoapHeader
{
    public string username;
    public string password;
}