Inconsistent Nancy testing when deserializing some json response.

error.cs

using System.Collections.Generic;
using System.Linq;
using Nancy;
using Nancy.Testing;
using Newtonsoft.Json;
using Shouldly;
using Xunit;

namespace ConsoleApplication4
{
    // install-package xunit
    // install-package Nancy.Testing
    // install-package newtonsoft.json

    public class SampleModule : NancyModule
    {
        public SampleModule() : base("/")
        {
            Get["/"] = _ =>
            {
                var model = new FakeData
                {
                    Message = "Something bad happened.",
                    Errors = new Dictionary<string, string>
                    {
                        {"notificationId", "blah blah blah"}
                    }
                };

                return Response.AsJson(model);
            };
        }
    }

    public class SampleRepo
    {
        [Fact]
        public void DoTest()
        {
            // Arrange.
            var browser = new Browser(with => { with.Module<SampleModule>(); });

            // Act.
            var result = browser.Get("/");

            // Assert.
            var modelWithBadKey = result.Body.DeserializeJson<FakeData>();
            var modelWoot = JsonConvert.DeserializeObject<FakeData>(result.Body.AsString());

            const string notificationKey = "notificationId";
            modelWoot.Errors.First().Key.ShouldBe(notificationKey);
            modelWithBadKey.Errors.First().Key.ShouldBe(notificationKey);
        }
    }

    public class FakeData
    {
        public string Message { get; set; }
        public IDictionary<string, string> Errors { get; set; }
    }
}