samba - Aug 2014 - our dns replication: working or not?

Hi,

I'm using the microsoft RSAT DNS Manager to look at our samba4 internal 
AD dns, and see that there are differences between the dns records on 
our two DC's. (sernet samba 4.1.7 & 4.1.9)

(for example: our DC2 still shows an old NS record for samba.domain.com 
with a DC that no longer exists. The NS info on DC3 is correct)

I assumed that DNS records would be replicated, since samba-tool drs 
showrepl shows no replication errors between the two DC's. (and last 
successful attempt was some minutes ago)

Also, when adding new users on one DC, they also show up on the other 
DC, so (at least some) replication is working.

I have read on this list, that sometimes ForestDnsZones and 
DomainDnsZones need to be 'helped', in order to start replicating, like:

samba-tool drs replicate DC2 DC3 DC=DomainDnsZones,DC=samba,DC=domain,DC=com

Now my questions are:

* isn't it strange that, even though 'samba-tool drs showrepl' shows
only success, there are DNS differences between DC2 and DC3?

* when both DC's already contain DNS stuff, is it safe to do something like:
samba-tool drs replicate DC3 DC2 DC=DomainDnsZones,DC=samba,...
and
samba-tool drs replicate DC2 DC3 DC=DomainDnsZones,DC=samba,DC=...

Will changes be 'merged', or will the first command wipe and replace the
DNS contents of DC3 with the records on DC2?

MJ