In the DNS template I changed the primary and first secondary name. As example, I changed ns1.whatever.com to dns1.whatever.com, likewise for the secondory.
A pre-existing client domain correctly reflects these changes in the master DNS when I use the tool dig. In the slave domain it stubbornly keeps showing the old DNS domain names. Any newly added domain correctly shows the the new DNS domain names in both master and slave.
I tried updating the serial number of the domain, but only after several times deleting and creating the domain I finally got them in sync. This is now still possible before I migrate domains but later, when the sever is in full production, how do a make this change without without having to delete domains?