From LedHed's Wiki
When transferring or seizing the PDC Emulator role remember to set the new PDC as the Authoritative Time Source.
Reference
http://blogs.technet.com/b/bpuhl/archive/2005/12/08/415827.aspx
http://www.networkworld.com/community/node/42190
http://technet.microsoft.com/en-us/library/cc784800%28v=ws.10%29.aspx