Are you by chance maybe using the name 'nic.io' ?
Code:
$ dig -x 193.223.78.212
; <<>> DiG 9.4.2-P2 <<>> -x 193.223.78.212
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 49795
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;212.78.223.193.in-addr.arpa. IN PTR
;; ANSWER SECTION:
212.78.223.193.in-addr.arpa. 86400 IN PTR www.nic.io.
;; Query time: 1493 msec
;; SERVER: 192.168.222.10#53(192.168.222.10)
;; WHEN: Mon Oct 28 23:31:49 2013
;; MSG SIZE rcvd: 69