DNS/DJBについて、ここに記述してください。

Returning NXDOMAIN for empty nonterminals is not a bug. 

http://www.ietf.org/mail-archive/web/dnsext/current/msg11084.html

archive:
http://marc.info/?t=130132703600002&r=1&w=2

{{{
Bottom line: On behalf of the millions of users who rely on my DNS
software (and other deployed software that signals empty nonterminals
with NXDOMAIN), I object to any attempt to change the definition of
NXDOMAIN from the RFC 2308/Vixie 1999/BIND 9/tinydns/etc. definition
into something that applies to subdomains. In particular, I object to
the dnsext-reimprove document.
}}}

Vixie:
  http://marc.info/?l=djbdns&m=126798819516512&w=2