NullReferenceException on mocking generic base class

Hi all,
I found a possible bug in TypeMock when mocking base generic class. Look at the following code:

        internal class BaseGeneric<T>
        {
            internal List<T> _collection = null;

            internal BaseGeneric()
            {
                _collection = new List<T>();
            }

            internal bool Apply()
            {
                foreach (T elem in _collection)
                {

                }

                return false;
            }
        }

        internal class Derived : BaseGeneric<int>
        {
            
        }

        [TestFixture]
        [ClearMocks]
        public class TestDerived
        {
            [Test]
            [VerifyMocks]
            public void TestBoo()
            {
                Mock<Derived> mock = MockManager.Mock<Derived>();
                mock.AlwaysReturn("Apply", true);

                Derived rules = new Derived();
                Assert.IsTrue(rules.Apply());
            }
        }

When running this test (pattern extracted from our code), I always receive the following stack:

System.NullReferenceException: Object reference not set to an instance of an object.
at BaseGeneric`1.Apply() in BaseGeneric.cs: line 19
at TestDerived.TestBoo() in BaseGeneric.cs: line 46
at TypeMock.MockManager.a(String A_0, String A_1, Object A_2, Object A_3, Boolean A_4, Object[] A_5)
at TypeMock.InternalMockManager.getReturn(Object that, String typeName, String methodName, Object methodParameters, Boolean isInjected)
at TestDerived.TestBoo() in BaseGeneric.cs: line 41 

Enviroment:
* TypeMock Isolator 5.3.0
* Visual Studio 2005

Please note that with TypeMock 5.0.0 all is working fine.
Please let me know if there is any workaround or planned fix for this problem.

Thanks