We recently upgraded our Windows primary domain controller to Windows Server 2012 R2 standard.
The roles were transferred, RID, PDC and Infrastructure.
All points to the new server.
All our domain controllers are GC servers.
The domain function level still shows as Windows Server 2003 (old DC), as does the forest function level.
The problem is that the old domain controller still overwrites domain functions.
For example: It replicates it's time for the domain and overwrites security policies set on the new domain controller.
Users authenticate to the new domain controller whilst the old PDC is switched off, although, when the old PDF is on, users still authenticate against the old PDC.
We would like to keep the old domain controller as backup, but the new domain controller should be authoritative.