Thanks for the replies. I just got this from the Support people, does this sound reasonable / plausible?:
Let me explain in detail, You have the [VPS] with us which is allocated to you with 2 IP address
The Name servers provided to your server are (ns1.domain.co.uk & ns2.domain.co.uk) and both are registered with the IP address as
ns1.domain.co.uk = 000.000.00.114
ns2.domain.co.uk = 000.000.00.115
If you ping the name servers they will show you pointing towards there respective given IP address.
Apart from this in terms of your reported issue, The IP address 000.000.00.114 behaves as a shared IP address for all the domains hosted on the same server. whenever you ping any domain hosted on your server this IP address will resolved. But if you check for the domain name "domain.co.uk" then its pointing to the 000.000.00.115 which means that the domain name is provided with a specific and dedicated IP address.
Unfortunately the IP address which is provided for your domain name "domain.net" is 000.000.00.115 which is already pointed for the ns2.domain.co.uk (name server), because of which your name server went to the cache of google. You can check for the IP address allocation on your server from the WHM
Login to the WHM >> Main >> IP Functions >> Show IP Address Usage
As of now if you wish to make it fix you need to either switch the domain name "domain.net" to the shared IP address 000.000.00.114 else you need to purchase another a new IP address which we will add to your server and you can then able to allocate with the dedicated IP address.
If you wish to change the domain name IP address you can do this from the WHM itself
Login to the WHM >> Main >> Account Functions >> Change Site's IP Address
You are requested to please provide us with your confirmation whether you wish to purchase a new IP address for the domain name or you wish to change it to the shared IP address itself.
Awaiting for your feedback.
[edited by: Andy_Langton at 9:00 am (utc) on May 24, 2012]
[edit reason] Anonymised domains [/edit]