Assume that you create a user account that has permissions to view items in a Microsoft SharePoint Foundation 2010 document library. You change the name of the user account, and then you perform a search for items in the document library by using the user account. In this situation, no items are returned.
This issue occurs if one of the following conditions is true:
SharePoint Foundation 2010 does not store the actual permissions of the current user account.
The Site Data web service does not send the UserKey attribute in the User element for user accounts that use claims-based authentication.
To resolve this issue, apply the following update:
2598304 Description of the SharePoint Foundation 2010 hotfix package (Wss-x-none.msp): April 24, 2012
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.