Very strange disk caching of zone file

[Redux Hostmaster]

I've tried numerous searches on this, and it has baffled all of us  
here, so I will post the scenario and look forward to any feedback  
offered.

DNS setup is as follows...

Primary and secondary nameservers, both holding master records,  
synced and zones reloaded whenever an update is made to a zone file.

Problem is noted on secondary nameserver, when any modifications made  
to /var/named/[our-reverse-zone].db do not take hold.

Here's how it was tested:

- PTR record added to zone file in question.
- Zone file reloaded, named also restarted for posterity
- /var/log/messages indicate zone is successfully loaded (serial is  
updated just to make sure it is grabbing the new zone on disk)
- dig @localhost -x [new IP in PTR] returns NXDOMAIN

The exact same testing behavior on the primary server results in  
success everytime.

The only solution we have been able to come up with, is renaming the  
zone file in /etc/named.conf -- and then copying the existing zone  
out of /var/named to the new name in /var/named.

Upon reloading the zone, a dig returns the appropriate results.

Any attempt to switch the zone file back to the original name results  
in failure.

Any input on this perplexing problem would be greatly appreciated.

Redux Hostmaster
Network Redux, LLC
hostmaster at networkredux.com
http://www.networkredux.com
Phone:  800-756-6518
Facsimile:  800-756-6518