An Infoworld article references a Technet post, where Microsoft comes clean about problems with Server 2003 and Server 2012 R2 running in the same domain. I don’t see this as an unusual situation since Server 2003 will reach end-of-life in July 2015 and I’m sure many IT folks are upgrading their infrastructure. Apparently, many system administrators are complaining about Kerberos lock-outs that won’t let their users login to the domain.
The unusual thing about the post is that Microsoft is very detailed in the reasons for the lock-outs and several workarounds for the problem. There’s also admission that the solutions don’t always work. Make sure you check out the post, especially if you have Windows Server 2003 and Server 2012 R2 running in the same domain.