Microsoft has released an update that fixess five issues in Team Foundation Server 2012 Update 1

This update fixes five issues in Team Foundation Server 2012 Update 1, including permission loss after attaching a team project collection or calling ChangeServerId, performance degradation for TFS servers with many groups, Identity Sync job failures, and NULL values in work item fields in the warehouse.

This update fixes 5 specific issues:

After attaching a team project collection, non-admin users may lose permissions to the collection.
After calling ChangeServerId from TfsConfig.exe, non-admin users may lose permissions to collections.
Performance is degraded for TFS servers that have many groups.
Identity Sync Job fails continually after upgrade due to NullReferenceException.
After upgrading to Team Foundation Server 2012, all work item fields which reference people will have NULL values for their latest revisions in the warehouse.

Note: After installing the patch, you will need to manually initiate a rebuild of the warehouse in order to correctly populate the fields which reference people for the latest revisions of work items. Please see this article for more information on how to rebuild the warehouse.

  Update to Team Foundation Server Update 1 (KB2795609)