It looks to me like the problem is that for all .sa.gov.au sub-domains
whois.ausregistry.net.au says

    Name Server:             ns.adelaide.edu.au
    Name Server IP:          129.127.40.3
    Name Server:             ns1.on.net
    Name Server:             ns2.on.net
    Name Server:             ns3.on.net
    Name Server:             arnie.systems.sa.gov.au
    Name Server IP:          203.26.120.3

which are the name servers for sa.gov.au, rather than the sub-domain
you query for.

For example
    whois -h whois.ausregistry.net.au adelaide.sa.gov.au
lists the name servers above.  But according to ns*.on.net
(which are authoritative name servers for sa.gov.au): 

    adelaide.sa.gov.au.     86400   IN      NS      ns0.mel.aone.net.au.
    adelaide.sa.gov.au.     86400   IN      NS      ns1.mel.aone.net.au.
    adelaide.sa.gov.au.     86400   IN      NS      ns2.syd.aone.net.au.

In the case of robe.sa.gov.au, the DNS servers at ns*.on.net say:
    robe.sa.gov.au.         86400   IN      NS      ns.seol.net.au.
    robe.sa.gov.au.         86400   IN      NS      ns2.seol.net.au.

I think the moral of this story is that whois.ausregistry.net.au is
not a good place to ask about DNS servers for sa.gov.au domains.

] At one stage seol.net.au were authoritive for a group of sa.gov.au domains
] including for example robe.sa.gov.au
] 
] As we were SOA, I obviously hosted the records for these domains. Every few
] months we run a whois against the domains we host to ensure that we only
] have records for domains we are SOA for. On deleting the records we found
] although we are not SOA, the servers listed in a whois must "Proxy" requests
] back to us, as in doing so caused the domains to no longer resolve.
] 
] Does anyone know if this is considered an ok practice ?
] 
] I have just relocated our nameservers and decided to drop ns.seol.net.au in
] favour of ns1.seol.net.au and ns2.seol.net.au.
] 
] As from what I guess the "proxy" setup in place at internode has a hardcoded
] reference to ns.seol.net.au for forwarding requests to, this has caused me
] to have to bring up ns.seol.net.au again (on a dialup as we now use use the
] c-class it once resided on for dialup customers)
] 
] Hope this doesnt sound a nonsense ... any light that can be shed on the
] matter would be greatly appreciated.
] 
] Cheers Tony
] 
] 
] Whois:
] 
] Domain Name: mountgambier.sa.gov.au
] Last Modified: Never Updated
] Registrar ID: R00004-AR
] Registrar Name: NOIE
] Status: ok
] 
] 
] Registrant: City of Mount Gambier
] Registrant ID: OTHER
] 
] 
] Registrant ROID: C0922352-AR
] Registrant Contact Name: THE MANAGER
] Registrant Email: city§mountgambier.sa.gov.au
] 
] 
] Tech ID: C0922354-AR
] Tech Name: Internode Professional Access
] Tech Email: aunic§internode.com.au
] 
] 
] Name Server: ns.adelaide.edu.au
] Name Server IP: 129.127.40.3
] Name Server: ns1.on.net
] Name Server: ns2.on.net
] Name Server: ns3.on.net
] Name Server: arnie.systems.sa.gov.au
] Name Server IP: 203.26.120.3
] 
] 
] 
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___________________________________________________________________________
 David Keegel <djk&#167;cybersource.com.au>  http://www.cyber.com.au/users/djk/
 Cybersource P/L: Linux/Unix Systems Administration Consulting/Contracting