The issues were documented here – http://blogs.technet.com/b/askds/archive/2014/07/23/it-turns-out-that-weird-things-can-happen-when-you-mix-windows-server-2003-and-windows-server-2012-r2-domain-controllers.aspx
The main issue is that users could not log on to the domain and Kerberos errors (EventID 4) were logged. This could lead to issues, and frustration, especially in migration situations.
The hotfix can be obtained here – http://support.microsoft.com/kb/2989971
2 thoughts on “Hotfix: Resolve Issues in mixed Windows Server 2003 and 2012R2 Domain Controller environments”
Where to apply the hotfix? on Windows 2012, Windows 2003 or computer with Windows 7
The hotfix states: “To resolve this issue, we have released a hotfix and an update rollup for Windows Server 2012 R2 in which Active Directory is installed.”
That means it should be installed on Windows Server 2012 R2.