Isolated behavior lost in DoInstead blocks?

using System;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using TypeMock.ArrangeActAssert;

namespace TypeMockTests
{
    [TestClass]
    public class TestInterfaceMockInDoInstead
    {
        [TestMethod, Isolated]
        public void TestFailsWhenIsolatedInDoInstead()
        {
            ISomeObject obj = Isolate.Fake.Instance<ISomeObject>();
            ISomeObject parentObj = Isolate.Fake.Instance<ISomeObject>();
            Isolate.WhenCalled(() => obj.Parent).WillReturn(parentObj);

            SomeClass someClass = Isolate.Fake.Instance<SomeClass>();

            // check that the Isolated behavior is working correctly
            Assert.AreEqual(parentObj, obj.Parent);

            Isolate.WhenCalled(() => someClass.DoSomething(null)).DoInstead(
                x =>
                {
                    // at this point, the Isolated behavior is lost for some reason
                    Assert.AreEqual(parentObj, obj.Parent);
                });

            someClass.DoSomething(obj);
        }

        public interface ISomeObject
        {
            ISomeObject Parent { get; }
        }

        public class SomeClass
        {
            public void DoSomething(ISomeObject obj)
            {
            }
        }
    }
}