Moq - cannot iterate through a hidden IEnumerable

We have a reasonably complicated interface hierarchy and I'm struggling to get Moq to do what I want it to.

I have an interface IReservation which extends IRulesReservation, and hides its enumerator with a new implementation of another type.

public interface IReservation : IRulesReservation
{
    new IEnumerator<IRoutePart> GetEnumerator();
}

IRulesReservation extends IEnumerable.

public interface IRulesReservation : IEnumerable<IRulesRoutePart>
{
}

The method I'm trying to test takes in an IReservation, but at various points needs to access the IEnumerable<IRulesRoutePart>. My Mock is setup like so:

m_mock = new Mock<IReservation>();
m_mock.As<IRulesReservation>().Setup(r => r.GetEnumerator()).Returns(routeParts.Select(rp => (IRules开发者_运维技巧RoutePart)rp).GetEnumerator());

In the example, routeParts is a list of IRouteParts that come from Mock<IRouteParts> objects that are setup with .As<IRulesRoutePart>().

Whenever I get to a bit of code in the function I'm testing that uses the enumerator, it steps over the iteration as though the collection was empty.

Am I doing something wrong in my setup? Or is Moq just unable to handle an enumerator that is hidden in this way?

Edit: some strange behaviour I've just noticed when running test code on the mock:

Assert.That((reservation.Object as IRulesReservation).Count() == 8);
Assert.That((reservation.Object as IEnumerable<IRulesRoutePart>).Count() == 8);

The first line will pass, but the second line will fail. I tried changing the mock to specifically setup an enumerator for IEnumerable<IRulesRoutePart>, but to no effect:

m_mock.As<IEnumerable<IRulesRoutePart>>().Setup(r => r.GetEnumerator()).Returns(routeParts.Select(rp => (IRulesRoutePart)rp).GetEnumerator());

Does the object that your setup returns actually have data? That's probably your problem.