Private Public DNS question

[sar1960 at mindspring.com]

I currently have an internal DNS server that supports internal queries.
This DNS server has the Internet root servers defined in the root.cache
file, so internal queries destined for the Internet will be resolved.  I
have a DNS server on a DMZ(public) network that resolves queries coming from
the Internet. The problem I have encountered is there are some names on the
Internet that I do not get resolution using my internal DNS server  but will
resolve using the DNS server on my DMZ.  With a sniffer on the DMZ I see the
DNS request leaving my internal network bound for the name server that is
authoritive for the request but I get no response.  If the query comes from
the DNS server on the DMZ it resovles. Any explaination would be a great
help.
--
Steve Redmond
steve.redmond at columbia.net