Router: 3640 running Version 12.4(13a) IP/FW/IDS

I have the router set up to be a basic dns caching/forwarding server,
and I have several IP HOST entries for my domains to serve the
internal IPs locally. The same domains exist on the internet with
public IPs. So I'm doing a very basic split DNS setup.

host domain.com 10.10.10.10

If I do an nslookup for domain.com, I get 10.10.10.10 back, perfect

My public DNS has a wildcard so if I do an nslookup for foo.domain.com
I get back the public IP, 200.200.200.200 which is expected.

However now my "show run" has
host domain.com 10.10.10.10 200.200.200.200

And nslookup to domain.com now returns 10.10.10.10, 200.200.200.200

Why the heck is it updating my host entry, especially when the lookup
was to a different host entirely? I would expect it to leave the
static entry alone and create a new dynamic/cached entry for foo.

In testing I found it only does this when I only specify the root
domain like that. If I do mail.domain.com 10.10.10.10 and do nslookup
for foo.mail.domain.com everything works as expected. So maybe its
confused that its a domain name without a hostname?

A wildcard host would be ideal but don't think it can be done. I
guess I could configure true split DNS in the router but that would
mean maintaining an external DNS server, which I do have but its
overkill.

This causes issues on my network as it load balances and half the time
doesn't work.