Either negative caching, or the ip6 is trimmed off
~$ dig jameshamilton.us NS
; <<>> DiG 9.4.2-P2.1 <<>> jameshamilton.us NS
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50015
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 4
;; QUESTION SECTION:
;jameshamilton.us. IN NS
;; ANSWER SECTION:
jameshamilton.us. 7190 IN NS ns1.mydomain.com.
jameshamilton.us. 7190 IN NS ns3.mydomain.com.
jameshamilton.us. 7190 IN NS ns2.mydomain.com.
jameshamilton.us. 7190 IN NS ns4.mydomain.com.
;; ADDITIONAL SECTION:
ns4.mydomain.com. 1790 IN A 63.251.83.74
ns1.mydomain.com. 1790 IN A 64.94.117.193
ns2.mydomain.com. 1790 IN A 64.94.31.67
ns3.mydomain.com. 1790 IN A 66.150.161.137