Mirrored DNS Servers, Some Addresses Not Found

[Grant]

I have BIND installed on 3 different computers, all three having the 
same configuration information.  I use to use WebMin to update each, but 
that was kind of a pain to have to go to three different systems to make 
a change.

I recently set it up with one being the primary (the server I make the 
changes on) and then the other two copying their configuration files 
from this one.  I have a cron script on the two secondary servers that 
stops BIND on that server, copies all the configuration files over 
(except rndc.key), and then restarts BIND.

For the most part, it works.  But something strange has been happening 
since doing this.  Some of the addresses (A) I have setup since doing 
this work for a while, and then can't be found, and then go back to 
working again.  Maybe they are not related, but this started happening 
when I started copying the configuration files.

Any ideas of what may be causing this?  Are there better ways to mirror 
DNS servers?