Problem w/ Forwarding Zone in Caching-Only Config

[Michael W. Fleming]

We're setting up a wireless printing service that uses
Zeroconf/bonjour/rendevouz dns entries. The product, Presto, has it's
own dns server for a private, on-campus only zone (presto.). We're
running bind 9.9 with a master server, three slaves and two caching-only
servers (anycasted to 136.168.255.2). We have the following in
named.conf (as per the vendor) on the caching-only servers.

zone "presto." {
      type forward;
      forward only;
      forwarders { 136.168.2.66; };
};

I manually added some required dns entries in our zone (as per vendor),
e.g.:

dig +short ptr b._dns-sd._udp.0.43.168.136.in-addr.arpa
0.43.168.136.dnssd.presto.

However, when I query the presto address, the query is sent to the
roots, not the presto server:

$ dig ptr 0.43.168.136.dnssd.presto.

; <<>> DiG 9.11.1 <<>> ptr 0.43.168.136.dnssd.presto.
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 46445
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;0.43.168.136.dnssd.presto.	IN	PTR

;; AUTHORITY SECTION:
.			86400	IN	SOA	a.root-servers.net. nstld.verisign-grs.com. 2017062002
1800 900 604800 86400

;; Query time: 2 msec
;; SERVER: 136.168.255.2#53(136.168.255.2)
;; WHEN: Tue Jun 20 10:04:25 PDT 2017
;; MSG SIZE  rcvd: 129

I am by no means a bind wizard. Any help would be appreciated.

Many thanks.

-- 
Michael Fleming, IT Networking, Datacenter & Telecom, CSU, Bakersfield