I don't think non public properties checking getters works

I have this method:

public class Mod
{
public void AddProperty(Property property)
{
if (property == null)
throw new ArgumentNullException("property");

this.Properties.Add(property);
}
}

Notice the properties call, which calls the getter. The following test fails to verify this, even though it gets called.

[TestFixture]
public class ModTest : Mod
{
[Test]
public void AddingPropertyToSubmoduleAddsElementsCorrectly()
{
//Arrange
var moduleFake = Isolate.Fake.Instance<ModTest>();
Isolate.SwapNextInstance<ModTest>();
Isolate.WhenCalled(() => moduleFake.AddProperty(new Property("Test", moduleFake))).CallOriginal();

var propertyFake = Isolate.Fake.Instance<Property>(Members.CallOriginal, ConstructorWillBe.Called);
Isolate.SwapNextInstance<Property>();

//Act
ModTesttest = new ModTest();
var property = new Property("Test", test);
test.AddProperty(property);

//Assert
Isolate.Verify.NonPublic.Property.WasCalledGet(moduleFake, "Properties");
}
}

Notice the test inherits from the class. The inheritance seems to be throwing it off.