Resolved: Windows Patch, for Windows, Causing Kerberos Authentication Issues
The affected Windows systems were found to be Windows 7, Server 2008 and 2008 R2. The Patches KB3147071, KB3149090 and KB3146706 have caused the Down-Level Logon method Domain\\UserName to incorrectly function against the PSU authentication realm. A support ticket is being submitted to Microsoft to resolve the bug.
The supported method of logon is to use firstname.lastname@example.org (the UPN logon method) which resolves this issue. This method works as expected against the PSU authentication realm.