How does zimbra redirect to the host that holds the user's mailstore.

In a situation I have presently, in a multiserver set up using 5RC1 on Fedora7, I have a two zimbra servers with everything installed except proxy.

I try to log into the zimbra-au.example.com (ldap is being replicated from zimbra-master.example.com to zimbra-au.example.com) and it tries to redirect me with an authtoken to zimbra-au.example.com.au. I try to log into zimbra-au and it redirects me to zimbra-au.example.com.au with an authtoken.

zimbra-au.example.com.au is a legitimate server on our network but it is not in the RC1 configuration (servers listed in the admin console on master-zimbra.example.com are zimbra-master.example.com and zimbra-au.example.com only). zimbra-au.hitwise.com.au is a standalone 4.5.7 zimbra test server.

Using firefox I have cleared all cookies and all other private data and restarted my browser.

Both hosts (zimbra-au.example.com and zimbra-master.example.com) resolve each other via dns correctly. DNS MX for example.com contain
example.com. MX 10 mail
example.com. MX 20 zimbra-au.example.com.
example.com. MX 20 zimbra-uk.example.com.
example.com. MX 30 zimbra-master.example.com.

[zimbra@zimbra-au ~]$ host zimbra-au
zimbra-au.example.com has address

[zimbra@zimbra-master ~]$ host zimbra-au
zimbra-au.example.com has address

How could it be redirecting to zimbra-au.example.com.au? As I say there is a legitimate host called zimbra-au.example.com.au but it definitely isn't in the zimbra-master configs.