I've a Forrest root we'll call ROOT and a child domain we'll call CHILD. I recently added a new 2008DC to the CHILD domain. It's not showing with a GUID CNAME record in the _msdcs.ROOT zone when I look at DNS from my CHILD domain DNS servers. I do see that record when I view DNS from my forest root DC. I also notice a CNAME record for a recently removed CHILD domain DC when viewing DNS from the CHILD domain DNS servers, but not on the ROOT DNS server.
I do see an event on my ROOT DC under the DNS Server event log; Event ID 4515 Source 4515, indicating I may have had another zone copy that conflicted.
So it would appear I have a problem in DNS replicating from the forest ROOT to my CHILD domain DNS servers. I'm not sure where to go from here in trouble shooting this.