MapValue works incorrectly with mapping extensions

MapValueTests.cs

#region Types for MapValueTest

public class Person
{
    public int Id { get; set; }
    public bool IsActive { get; set; }
}

public class SecurityDbMappingSchema : MappingSchema
{
    public SecurityDbMappingSchema()
    {
        Extensions = TypeExtension.GetExtensions("SecurityMap.xml");
    }
}

public class SecurityDbManager : DbManager
{
    public const string DefaultConnStringName = "ProtoDB";

    public SecurityDbManager(string connStringName)
        : base(connStringName)
    {
        InitializeMappingSchema();
    }

    private void InitializeMappingSchema()
    {
        MappingSchema = new SecurityDbMappingSchema();
    }

    public SecurityDbManager()
        : this(DefaultConnStringName)
    {
    }

    public Table<Person> Persons
    {
        get { return GetTable<Person>(); }
    }
}

#endregion

private const string ConnString =
    "Network Address=192.168.0.128;User ID=pWriter;PWD=pass;Initial Catalog=ProtoDB;Connect Timeout=300";

[TestMethod]
public void TestMapValueAttribute_Passes()
{
    string result = null;
    DbManager.AddConnectionString("ProtoDB", ConnString);
    
    //Record is assumed to exist
    var p = new Person { IsActive = true, Id = 38361 };

    using (var db = new SecurityDbManager())
    {
        db.Update(new[] { p }.AsEnumerable());

        db.SetCommand(CommandType.Text, "SELECT [IsActive] FROM [Persons] WHERE [UserId]=" + p.Id);
        result = (string) db.ExecuteScalar();
    }

    Assert.AreEqual("Y", result);
}

[TestMethod]
public void TestMapValueAttribute_Fails()
{
    string result = null;
    DbManager.AddConnectionString("ProtoDB", ConnString);
    
    //Record is assumed to exist
    var p = new Person { IsActive = true, Id = 38361 };

    using (var db = new SecurityDbManager())
    {
        db.Update(p);

        db.SetCommand(CommandType.Text, "SELECT [IsActive] FROM [Persons] WHERE [UserId]=" + p.Id);
        result = (string)db.ExecuteScalar();
    }

    Assert.AreEqual("Y", result);
}