Static constructor unexpectedly called in AAA

I am unit testing SharePoint code that calls methods of the SPUtility class. My tests fail because the SPUtility class's static ctor throws a null reference exception, even though I have mocked the static ctor. Here is a minimal repro, using a static class of my own instead of SPUtility (just in case there was something odd about the SPUtility class):

namespace TypeMockTest
{
    using System;
    using Microsoft.VisualStudio.TestTools.UnitTesting;
    using TypeMock.ArrangeActAssert;

    public static class MyStaticClass
    {
        static MyStaticClass()
        {
            throw new Exception("MyStaticClass cctor should not be called.");
        }

        public static string Foo()
        {
            return "Foo";
        }
    }

    [TestClass]
    public class StaticConstructorFailure
    {
        [TestMethod, Isolated]
        public void StaticConstructorFails()
        {
            Isolate.Fake.StaticConstructor(typeof(MyStaticClass));
            Isolate.Fake.StaticMethods(typeof(MyStaticClass));

            Isolate.WhenCalled(() => MyStaticClass.Foo()).WillReturn("Bar");
        }
    }
}

This test fails because the "Isolate.WhenCalled" line throws the exception from the static ctor, even though the static ctor is mocked.

Thanks,
Larry