There are lots of reasons not to list a slave name server in a zone’s NS records; you’ve made it a slave because the resolvers that query it frequently look up records in the zone, but you don’t want other name servers querying it, for example. See Section 7.5 for instructions on configuring a stealth slave.
However, you probably want your stealth slave to be alerted of changes to the zone as quickly as the other slaves for the zone.
Something is always changing on your network -- new workstations arrive, you finally retire or sell the relic, or you move a host to a different network. First we'll discuss how to make the changes manually. Actually, we recommend that you use a tool to create the zone data files -- we were kidding about that wimp stuff, okay?
Each change means that zone data files must be modified. Or at least use a tool to increment the serial number for you.
Although what I wrote before and what's written in the log, it's obvious that this error occurs after a notify, that for some reason isn't logged.