yes/no should be a string, not a boolean. I hate yaml.

defaults/main.yml

@@ -11,11 +11,11 @@ powerdns:
     "include-dir": "/etc/powerdns/pdns.d"
     "launch":
     - bind
-    "master": no
+    "master": "no"
     "reuseport": "yes"
     "setgid": pdns
     "setuid": pdns
-    "slave": no
+    "slave": "no"
     "soa-minimum-ttl": 300
     "tcp-control-secret": "{{ lookup('password', '/dev/null length=64') }}"
     "version-string": "1"