Robert A. Pickering Jr. was known to have said:
What if I registered a domain against your nameservers and then
advertised it? What would your nameservers do with the lame delegations?
I've had lame delegations really mess up my DNS servers. They spend all
their time asking the top-level servers, who just point back to them.
We recently had a downstream customer of ours tell his customer
that it was okay to use our nameservers as his secondary for
his domains. About 60 of them.
The InterNIC appears to have no clear policy on removing the NS
records that point to an unwilling DNS server. At one time I
actually sent a message off to questions(?)@internic.net on this
issue, but never received a response.
Our solution was to provide empty DNS records to prevent lame
delegation problems.