strange behavior in vs2012 + r#

DynamicTest.cs

    [TestFixture]
    public class DynamicTest
    {
        public class Dto
        {
            public string Value { get; set; }
        }

        public Dto ToDto(dynamic d)
        {
            return new Dto();
        }

        [Test]
        public void dto_is_typed()
        {
            // var is Dto
            var dto = ToDto(new { dummy = true });
            dto.Value = "val";

            Assert.Inconclusive("yust for intellisense test");
        }

        [Test]
        public void dto_is_dynamic_inside_an_action_with_dynamic_type()
        {
            Action<dynamic> act = o =>
                {
                    // dto is dynamic
                    var dto = ToDto(o);
                    dto.ThisIsNotAProperty = 100;
                };


            var ex = Assert.Throws<Microsoft.CSharp.RuntimeBinder.RuntimeBinderException>(() =>
                {
                    act(new {dummy = true});
                });

            Assert.IsTrue(ex.Message.EndsWith("does not contain a definition for 'ThisIsNotAProperty'"));
        }
    }