这是在LINQ一个众所周知的缺陷，以SQL。

This is a well-known bug in LINQ to SQL.

https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=351358

有对于问题的修补程序。

There is a hotfix for the issue.

http://support.microsoft.com/hotfix/KBHotfix.aspx?kbnum=963657&kbln=en-us