Specifically, if I do this dig:
dig @a0.org.afilias-nst.info isc.org
it's supposed to return the authoritative name servers for isc.org, but it frequently doesn't for the machines on my network. I've tried it from an Amazon EC2 instance and don't see any problems from there, but I can't figure out why there would be a difference based on where I perform the query from.
What should I be looking at next? If it is indeed an issue with that particular server, how would I report it?