Mocking a generic method on a static class in 4.2.4

public static class AgentFactory
{
        private static Dictionary<string, IAgent> _agentDictionary;

        static AgentFactory()
        {
            _agentDictionary = new Dictionary<string, IAgent>();
        }

        public static T GetAgent<T>() where T : IAgent
        {
            if (!_agentDictionary.ContainsKey(typeof(T).Name))
            {
                _agentDictionary.Add(typeof(T).Name, LoadAgent<T>());
            }
            return (T)_agentDictionary[typeof(T).Name];
        }
}

[TestFixture]
public class AccountAgentTests
{
    private Mock _agentFactoryMock;
    private MockObject _accountAgentMock;

    [SetUp]
    public void Setup()
    {
        _agentFactoryMock = MockManager.Mock(typeof(AgentFactory));
        _accountAgentMock = MockManager.MockObject(typeof(IAccountAgent));

        _agentFactoryMock.ExpectAndReturn("GetAgent", _accountAgentMock.MockedInstance, typeof(IAccountAgent));

        [... set up other mocks here ...]
    }
}

------ Test started: Assembly: MyCompany.AccountAgent.UnitTests.dll ------

TestCase 'MyCompany.AccountAgent.UnitTests.AccountAgentTests.MyUnitTest'

failed: TypeMock.TypeMockException : 

*** Method GetAgent in type MyCompany.Agent.Factory.AgentFactory returns  and not TypeMock.Mock+a.
       at w.b(Type A_0, String A_1, Type A_2, Type[] A_3)
       at TypeMock.Mock.a(String A_0, Object A_1, Boolean A_2, Boolean A_3, Int32 A_4, Type[] A_5)
       at TypeMock.Mock.ExpectAndReturn(String method, Object ret, Int32 timesToRun, Type[] genericTypes)
       at TypeMock.Mock.ExpectAndReturn(String method, Object ret, Type[] genericTypes)
       MyCompanyAccountAgentUnitTestsAccountAgentTests.cs(38,0): at MyCompany.AccountAgent.UnitTests.AccountAgentTests.Setup()