[CentOS] Zone file not written to slave DNS server

I have mostly succeeded in getting master and slave DNS servers operational.  Mostly, because the zone file is not written when a zone is updated on the master server when the notify and transfer process happens.

The slave DNS server gets the changes to the modified zone, but the slave zone file remains as before. I've found a few tutorials and lots of discussions, many of which talk about the slave's zone file getting written upon transfer, but none mention what configuration option would cause the slave's files to get updated.

The master is on a Cantos 6 server and the slave is on a Cantos 7 machine.

Any ideas?

Emmett