DNS64 synthesis not working for CNAME responses

Using kresd 1.2.6 on Turris Omnia, I've set up DNS64 using this snippet:

modules.load('dns64')
dns64.config('64:ff9b::')

It works well mostly but somehow it fails to synthetise AAAA response if the answer is indirected by a CNAME. For instance:

$ dig www.regiojet.cz aaaa

; <<>> DiG 9.11.0-P3 <<>> www.regiojet.cz aaaa
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 29320
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.regiojet.cz.               IN      AAAA

;; ANSWER SECTION:
www.regiojet.cz.        3310    IN      CNAME   brn-web02.sa.cz.

;; Query time: 3 msec
;; SERVER: 2001:718:e:ed14::1#53(2001:718:e:ed14::1)
;; WHEN: So čen 03 14:53:53 CEST 2017
;; MSG SIZE  rcvd: 71