Orleans Test Problem

gistfile1.txt

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Nest;
using Orleans;

namespace Test
{
    public interface ITestGrain : Orleans.IGrainWithIntegerKey
    {
        Task<TestObject> Get();
    }

    class TestGrain : Grain, ITestGrain
    {
        public Task<TestObject> Get()
        {
            var toc = new TestObjectChild();
            return Task.FromResult((TestObject)toc);
        }
    }

    [Serializable]
    public class TestObject
    {
        public TestProperty Prop { get; set; }
    }

    [Serializable]
    public class TestObjectChild : TestObject
    {
        public new exTestProperty Prop
        {
            get { return (exTestProperty)base.Prop; }
            set { base.Prop = value; }
        }
    }

    [Serializable]
    public class TestProperty
    {
        public int IntProp { get; set; }
        public string StringProp { get; set; }
    }

    [Serializable]
    public class exTestProperty : TestProperty
    {
        public int StringProp2 { get; set; }
    }
}