FakeDB Field Vanish

using System;
using FluentAssertions;
using Moq;
using NUnit.Framework;
using Sitecore.Data;
using Sitecore.Data.Items;
using Sitecore.FakeDb;

namespace NYL.UnitTests.FakeDB
{
    [TestFixture]
    public class FakeDbFieldValueTest
    {
        private readonly Mock<IRepository> _repo = new Mock<IRepository>();
        private readonly ID _tplId = ID.NewID;
        private readonly ID _fieldId = ID.NewID;
        private readonly string _fieldName = "F";

        [SetUp]
        public void SetUp()
        {
            //database = FakeDatabase();
            _repo.Setup(m => m.GetListOfItems()).Returns(Mock_GetListOfItems());
        }

        [Test]
        public void Test_FakeDbFieldRetention()
        {
            using (var db = FakeDatabase())
            {
                // arrange
                var items = _repo.Object.GetListOfItems();

                // assert
                items.Should().NotBeNull();

                foreach (var item in items)
                {
                    // Fields are null after passed back through mock
                    item.Fields[_fieldName].Should().NotBeNull();
                    item[_fieldName].Should().NotBeNullOrEmpty();
                }
            }
        }

        private Db FakeDatabase()
        {
            return new Db
            {
                new DbTemplate("Child Tpl", _tplId)
                {
                    new DbField(_fieldName, _fieldId)
                },
                new DbItem("Home")
                {
                    new DbItem("First Child", ID.NewID, _tplId)
                    {
                        {_fieldName, "Value One"}
                    },
                    new DbItem("Second Child", ID.NewID, _tplId)
                    {
                        {_fieldName, "Value Two"}
                    }
                }
            };
        }

        private Item[] Mock_GetListOfItems()
        {
            using (var db = FakeDatabase())
            {
                var query = string.Format("fast:/sitecore/content/Home//*[@@templateid = '{0}']", _tplId);
                var items = db.Database.SelectItems(query);

                foreach (var item in items)
                {
                    // Field Values render fine at creation
                    item.Fields[_fieldName].Should().NotBeNull();
                    item[_fieldName].Should().NotBeNullOrEmpty();
                }

                return items;
            }
        }
    }

    public interface IRepository
    {
        Item[] GetListOfItems();
    }
}