Change IP of Nameserver

[cyon]

we need to take one of our servers offline for some time, unfortunately it's the one that hosts our second Nameserver.
Therefore we would like to use another server to host that nameserver.

We changed /etc/nameserverips, edited the DNS zone to our best knowledge and requested the change of IP with our registrar, which has been confirmed a couple of houres ago, and is active by now.

But for some reason we can't ping or reach in any other way the new nameserver.

The only clue we can offer is that on the old server in /etc/namersverips there are more entries than just the 2 expected ones (NS1 and NS2).
There is an additional very persistent entry for the old IP, that doesn't vanish, even when the file is edited manually. The entry just keeps getting recreated immediately.
Also there is an entry that says: 123.123.123.12=0, keeps also reappearing.

Could this be the reason NS2 isn't reachable??
Any guess as to why this happens?

Or did we simply forget to change a crucial setting?

Sorry for the complicated description, if necessary I'll try to rephrase

Thanks in advance for any input!

/update: just discovered this: I deleted /etc/namersverips manually ( once again, just for the fun of it ) and this time it looked like it worked, there were no other/new entries created.
But when checking in WHM > Manage Nameserver IPs the entries were (still?) there.

Under "Manage Nameserver IPs" the file /etc/nameserverips is accessed, right? so there should at least be the same information...?
Some sort of sync error?
Or am I just mistaken about the relation between namserverips and "Manage..."?