Shouldn't this test pass:

[TestMethod]
public void derived_message_subscription()
{
    bool handled = false;
    Messenger.Default.Register<GenericMessage<baseClass>>(this, true, (msg) => handled = true);
    Messenger.Default.Send(new GenericMessage<testClass>(new testClass()));
    Assert.IsTrue(handled);
}

public abstract class baseClass { }
public class testClass : baseClass { }

I have to receive all messages for classes that inherits from one base class. MVVMLight has bool property receiveDerivedMessagesToo in Register method, but it seems to me that it isn't working.