LinqDataSource与datetime一起用出现"System.Data.Linq.ChangeConflictException: Row not found or changed"

表结构:

CREATE   TABLE   [ dbo ] . [ Table1 ] (
         [ Id ]   [ int ]   NOT   NULL ,
         [ TimeCreated ]   [ datetime ]   NOT   NULL ,
  CONSTRAINT   [ PK_Table1 ]   PRIMARY   KEY   CLUSTERED
(
         [ Id ]   ASC
) WITH  (IGNORE_DUP_KEY  =   OFF )  ON   [ PRIMARY ]
)  ON   [ PRIMARY ]  

insert   into  table1(id, timecreated)  values ( 1 ,  getdate ()) 

Aspx:

  <% @ Page Language = " C# "  AutoEventWireup = " true "  CodeBehind = " Cus.aspx.cs "
Inherits = " RfqMan4.Cus "   %>

<! DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://
www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" >

< html  xmlns ="http://www.w3.org/1999/xhtml"   >
< head  runat ="server" >
     < title > Untitled Page </ title >
</ head >
< body >
     < form  id ="form1"  runat ="server" >
     < div >

         < asp:GridView  ID ="GridView1"  runat ="server"
AutoGenerateColumns ="False"
            DataSourceID ="LinqDataSource1"  DataKeyNames ="id" >
             < columns >
                 < asp:commandfield  ShowEditButton ="True" ></
asp:commandfield >
                 < asp:boundfield  DataField ="id"  HeaderText ="id"
ReadOnly ="True"
                    SortExpression ="id" ></ asp:boundfield >
                 < asp:boundfield  DataField ="TimeCreated"
HeaderText ="TimeCreated"
                    SortExpression ="TimeCreated" ></ asp:boundfield >
             </ columns >
         </ asp:GridView >
         < asp:LinqDataSource  ID ="LinqDataSource1"  runat ="server"
            ContextTypeName ="RfqMan4.Components.RfqManDataContext"
EnableDelete ="True"
            EnableInsert ="True"  EnableUpdate ="True"
TableName ="Table1s" >
         </ asp:LinqDataSource >
     </ div >
     </ form >
</ body >
</ html >  

每次试图更新时都会抛出ChangeConflictException异常.
奇怪的是如果把第二个列换成除datetime以外的类型,比如int, nvarchar等都能正常工作; 而Northwind里同样包含datetime列的Orders表也没有问题.
已经证实了这个问题与Id列是否自增,datetime列是否可为空,是否有默认值无关--无论任何情况下都会出现.
这个是bug,还是我忘了哪一步?