Throwing derived exceptions with Natural Mocks

Hi,

I was wondering if the following exception throwing implementation is intended.

    public class ObjectUnderTest
    {
        public void MethodUnderTest()
        {
        }
    }

    public class DerivedException : Exception
    {
        public DerivedException()
            : base()
        {
        }

        public DerivedException(string message)
            : base(message)
        {
        }
    }

    [TestFixture]
    public class TestHarness
    {
        [Test]
        [ExpectedException(typeof(Exception))]
        public void WorkingExceptionTest()
        {
            // Create the object to be tested
            ObjectUnderTest obj = new ObjectUnderTest();

            // Start mocking
            using (RecordExpectations recorder = new RecordExpectations())
            {
                obj.MethodUnderTest();
                recorder.Throw(new Exception("TypeMock test"));
            }

            // Invoke method
            obj.MethodUnderTest();

            // Fails if exception not thrown
            Assert.Fail("Exception not thrown");
        }

        [Test]
        public void FailingExceptionTest()
        {
            // Create the object to be tested
            ObjectUnderTest obj = new ObjectUnderTest();

            // Start mocking
            using (RecordExpectations recorder = new RecordExpectations())
            {
                obj.MethodUnderTest();
                // COMMENT
                // I think that the DerivedException creation is being mocked???
                recorder.Throw(new DerivedException("TypeMock test"));
            }

            // Invoke method
            obj.MethodUnderTest();

            // Fails if exception not thrown
            // TEST FAILS HERE
            Assert.Fail("Exception not thrown");
        }
    }

The first test passes as per the documentation and provided examples :)
The second test creates a derived exception to be returned but this is not being thrown when the method is invoked. The failure assertion is being generated. I suspect that the creation of the derived exception may be mocked but this is a guess.

Could you please shed some light on this issue?

Thanks
Paul