Serializing a List<Interface> Property

Hi there,

I was trying to serialize an object with a List<Interface> as
property. If I do this i get an exception. when I add an extra proerty
with type object[] to my class and mark the original property with
[XmlIgnore] it works.
Is there a bettert way to do this without adding this property?

Thanks in advance
Roman

Code:

using System;
using System.Collections.Generic;
using System.Text;
using System.Xml.Serialization;
using System.Xml;

namespace SerializeTest
{
  public class Program
  {
    static void Main(string[] args)
    {
      // Create objects
      MainClass cm = new MainClass();

      cm.TestList.Add(new Test1());

      // Try to serialize MainClass
      XmlTextWriter writer = new XmlTextWriter(Console.Out);

      XmlSerializer ser = new XmlSerializer(typeof(MainClass), new Type
[]{typeof(Test1)});
      ser.Serialize(writer, cm);

      Console.ReadLine();

    }
  }

  [Serializable]
  public class MainClass
  {
    private List<ITest> _test = new List<ITest>();

    public object[] TestListO
    {
      get
      {
        return (object[])_test.ToArray();
      }
      set
      {
        foreach (object o in value)
        {
          if (o is ITest
            && !_test.Contains((ITest)o))
          {
            _test.Add((ITest)o);
          }
        }
      }
    }

    [XmlIgnore]
    public List<ITest> TestList
    {
      get { return _test; }
      set { _test = value; }
    }
  }

  [Serializable]
  public class Test1 : ITest
  {

    #region ITest Members

    public void Test()
    {
      Console.WriteLine(this.GetType().Name);
    }

    #endregion
  }

  public interface ITest
  {
    void Test();
  }
}