another question about the glue

[PANG J.]

h.gtld-servers.net is one of the net domain's NS servers.
As the info below:

$ dig mydots.net @h.gtld-servers.net

; <<>> DiG 9.4.2-P2.1 <<>> mydots.net @h.gtld-servers.net
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 57902
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 2, ADDITIONAL: 2
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;mydots.net.                    IN      A

;; AUTHORITY SECTION:
mydots.net.             172800  IN      NS      ns1.dnsbed.com.
mydots.net.             172800  IN      NS      ns2.dnsbed.com.

;; ADDITIONAL SECTION:
ns1.dnsbed.com.         172800  IN      A       74.117.233.4
ns2.dnsbed.com.         172800  IN      A       204.152.196.108

;; Query time: 279 msec
;; SERVER: 192.54.112.30#53(192.54.112.30)
;; WHEN: Sat Jul  2 03:25:41 2011
;; MSG SIZE  rcvd: 106


Why the "net" zone has the glue for the servers which are in the "com" zone?

Thank you.