25 June 2015
It turns out that weird things can happen when you mix Windows Server 2003 and Windows Server 2012 R2 DCs
UPDATE: The hotfix is now available for this issue! Get it at http://support.microsoft.com/kb/2989971
1. When any domain user tries to log on to their computer, the logon may fail with “unknown username or bad password”. Only local logons are successful.
2. Operating Systems on which the issue has been seen: Windows 7, WS2008 R2, WS2012 R2
3. This can affect Clients and Servers(including Domain Controllers)
4. This problem specifically occurs after the affected machine has changed its password. It can vary from a few minutes to a few hours post the change before the symptoms manifest