Test Class cannot be Derived from other Test Class

Try the following production code

    public abstract class BaseClass
    {

        public int Version
        {
            get
            {

                return 1;
            }

        }

        public string FixString
        {
            get;
            set;
        }

        public BaseClass()
        {
            FixString = "hello";
        }
    }


    public class DeriveClass: BaseClass
    {


        public DeriveClass():base()
        {

        }
    }

And the following test code

   [TestFixture]
    public class BaseClassTest<T>
        where T:BaseClass
    {

        public T BaseClassObj
        {
            get;set;
        }
    }
    [TestFixture, Isolated]
    public class DeriveClassTest:BaseClassTest<DeriveClass>
    {
        [Test]
        public void Test1()
        {
            BaseClassObj = new DeriveClass();
            Isolate.WhenCalled(() => BaseClassObj.Version)
                .WillReturn(5);
            Assert.AreEqual("hello", BaseClassObj.FixString);
        }
    }

The test fails, even though it should pass.

It seems that derived test class with generics will cause problem.