DNS and 2 NICs

I've got a DNS server that has two NIC's installed. The reason why is
because it has to act as a firewall for a few PC's so one adapter is
public and one is private. The DNS information on the PC is for the
public side only. The internal DNS is a seperate server. When the name
for itself is used out in the internet world sometimes it tries to use the
private NIC's IP. That's not even configured in the bind server! Hmm..
Any ideas? I've already turned the listen-on var to the public IP.