Network Gear that "helps" with DNS

I've noticed some unpredictable behavior when doing queries from
inside our network.

This includes the following:
dig some-name.com @ns.some-outside-server.com
returns an INTERNAL address.

When I access a host from outside our internal network and do the same
thing, I get the expected address.

This leads me to believe that within the internal network, some piece
of network gear is intercepting my query and providing an answer it
thinks should be provided.

We have mostly cisco gear, including pix firewalls. Does anyone know
of network gear that would do that? If it's a pix, where can one find
the settings for this?
=== Al