ADO.NET Entity Framework beta 3和Linq to SQL在缓存处理上的不同

//下面是使用LinQ to SQL 的例子，context2是派生自System.Data.Linq.DataContext的实例
ErpLinQContextDataContext context2 = new ErpLinQContextDataContext();
//SQLServer事件探查器拦截到SQL语句的执行
//exec sp_executesql N'SELECT TOP 1 [t0].[emp_id], [t0].[fname],
[t0].[minit], [t0].[lname], 
//                         [t0].[job_id], [t0].[job_lvl],
[t0].[pub_id], [t0].[hire_date]
//FROM [dbo].[employee] AS [t0]
//WHERE [t0].[emp_id] = @p0', N'@p0 varchar(9)', @p0 = 'PMA42628M'
employee p3 = context2.employees.First(p => p.emp_id == "PMA42628M");
//当我再次执行相同的查询时，LinQ to SQL 不再向SQL Server发送查询了。
employee p4 = context2.employees.First(p => p.emp_id == "PMA42628M");

//返回的对象是同一个实例
bool b2 = object.ReferenceEquals(p3, p4); //=true;
p3.lname = "New Last Name";
bool b4 = (p4.lname == "New Last Name");  //=true;

//pubsEntites是 ADO.NET Entity Framework 的System.Data.Objects.ObjectContext派生对象
pubsEntities context = new pubsEntities();
//下面语句执行时，SQLServer事件探查器拦截到SQL的执行
//SELECT TOP 1 [Extent1].[emp_id] AS [emp_id], [Extent1].[fname] AS [fname], 
[Extent1].[lname] AS [lname], 
//             [Extent1].[hire_date] AS [hire_date], [Extent1].[job_id] AS
[job_id], [Extent1].[pub_id] AS [pub_id]
//FROM [dbo].[employee] AS [Extent1]
//WHERE N'PMA42628M' = [Extent1].[emp_id]
Employee p1 = context.EmployeeSet.First(p => p.EmployeeId == "PMA42628M");
//SQLServer事件探查器 发现SQL再次被执行
Employee p2 = context.EmployeeSet.First(p => p.EmployeeId == "PMA42628M");
//测试发现，虽然ADO.NET Entity Framework执行了两次SQL，但是他们却返回了完全相同的实例
bool b1 = object.ReferenceEquals(p1, p2); // = true;

//如果使用不同的上下文更新的数据，
pubsEntities context4 = new pubsEntities();
Employee p10 = context4.EmployeeSet.First(p => p.EmployeeId == "PMA42628M");
p10.LastName = "Context4 changed data";
context4.SaveChanges();
//旧的context再次查询时。
Employee p11 = context.EmployeeSet.First(p => p.EmployeeId == "PMA42628M");
b1 = object.ReferenceEquals(p1, p11); //= true   why??
b1 = (p11.LastName == "Context4 changed data"); //= false  
p11.LastName = "New Last Name"