[SAGE] Question on DNS and reverse lookups

[Mike Noble <mgnoble@cox.net>]

When I do a dig on my domain name, I get the following:

; <<>> DiG 9.2.3rc2 <<>> rfmagic.com
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2338
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 0

;; QUESTION SECTION:
;rfmagic.com.                   IN      A

;; ANSWER SECTION:
rfmagic.com.            3600    IN      A       64.66.31.205

;; AUTHORITY SECTION:
rfmagic.com.            3600    IN      NS      ns2.rfmagic.com.
rfmagic.com.            3600    IN      NS      ns1.rfmagic.com.

;; Query time: 43 msec
;; SERVER: 68.6.16.25#53(68.6.16.25)
;; WHEN: Thu Jan  1 21:06:24 2004
;; MSG SIZE  rcvd: 81

Now if I do a reverse on the address, I get:

; <<>> DiG 9.2.3rc2 <<>> -x 64.66.31.205
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 44361
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 1

;; QUESTION SECTION:
;205.31.66.64.in-addr.arpa.     IN      PTR

;; ANSWER SECTION:
205.31.66.64.in-addr.arpa. 86208 IN     PTR     mhrf.rf-magic.com.

;; AUTHORITY SECTION:
31.66.64.in-addr.arpa.  86208   IN      NS      ns1.4d.net.
31.66.64.in-addr.arpa.  86208   IN      NS      ns2.4d.net.

;; ADDITIONAL SECTION:
ns1.4d.net.             85821   IN      A       64.66.0.10

;; Query time: 14 msec
;; SERVER: 68.6.16.25#53(68.6.16.25)
;; WHEN: Thu Jan  1 21:07:13 2004
;; MSG SIZE  rcvd: 132


With the reverse I get a different Authority section. 
Why would the reverse give a different Authority section?

Thanks,
Mike