How to return one Mock object from another

using System.Windows.Forms;
using NUnit.Framework;
using TypeMock;

//Strange.Class1.Test3 : TypeMock.TypeMockException : 
//*** Method Create in type Strange.Factory returns Strange.A and not TypeMock.Mock+a.

namespace Strange
{
   [TestFixture]
   public class Class1
   {
      [SetUp]
      public void SetUpMocker()
      {
         MockManager.Init();
      }
      [Test]  // We want to avoid running this test by using mock objects
      public void NonAutomaticTest()
      {
         ClassUnderTest cut = new ClassUnderTest();
         cut.MethodUnderTest();
      }
      [Test]
      public void Test3()
      {
         Mock sayer = MockManager.Mock(typeof(Sayer));
         Mock factory = MockManager.Mock(typeof(Factory));
         factory.ExpectAndReturn("Create", sayer.MockedInstance as A);
         sayer.ExpectCall("SayA");
         ClassUnderTest cut = new ClassUnderTest();
         cut.MethodUnderTest();
         MockManager.Verify();
      }
   }

   public class ClassUnderTest
   {
      public void MethodUnderTest()
      {
         Factory factory = new Factory();
         A a = factory.Create();
         a.SayA();
      }
   }

   public interface A
   {
      void SayA();
   }

   public class Sayer : A
   {
      public void SayA()
      {
         MessageBox.Show("A", "Message");
      }
   }

   public class Factory
   {
      public A Create()
      {
         return new Sayer();
      }
   }
}