[nznog] DNS serving IPs outside controlled range

I have a...friend, let's say...who operates a DNS server at a small ISP. In a few of the zone files, there are A records that resolve to IP addresses outside of the Class C that my..friend...controls. My friend has been told that this is "against the rules" and that it is "causing problems". Questions: - is resolving an A record outwith the delegated IP range "against the rules"? - if so, is there any documentation of the rules? - what potential problems could this cause to the network that contains the IP address to which the A records point? Thanks for any advice. Regards, Stu