If I ping something that has A and AAAA, it pings the A record, and both the A and AAAA records appear in /ip dns cache print!
I think this is the DNS server giving everything it knows "just to be nice"
root ~ # dig A orange.kame.net
; <<>> DiG 9.9.5-3ubuntu0.6-Ubuntu <<>> A orange.kame.net
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 65285
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 4
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;orange.kame.net. IN A
;; ANSWER SECTION:
orange.kame.net. 86283 IN A 188.8.131.52
;; AUTHORITY SECTION:
kame.net. 172678 IN NS orange.kame.net.
kame.net. 172678 IN NS mango.itojun.org.
;; ADDITIONAL SECTION:
mango.itojun.org. 86278 IN A 184.108.40.206
mango.itojun.org. 86278 IN AAAA 2001:2f0:0:8800::1:1
orange.kame.net. 172678 IN AAAA 2001:200:dff:fff1:216:3eff:feb1:44d7
;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Thu Jan 07 15:07:43 CST 2016
;; MSG SIZE rcvd: 176
See how the only thing I requested was an A record, but the server threw in the NS records and the AAAA records here? (I think this is because orange.kame.net is also an NS record, in this case, but often times, the hostname you are pinging to is a CNAME which will also cause servers to proactively hand you the answers to the logical next question - i.e. what are the A/AAAA records for the name the alias points to?)
I think the ping client doesn't bother to try resolving AAAA-only hostnames at all... it just sends an A record request and if the query fails, then it is done. It does
know what an IPv6 address is though - so if you ping that, it will recognize it and work properly.
The same is true of the winbox ping tool. If I type a v6-only hostname into the tool, it throws an error that a valid IP address was expected, but if I type a v4-capable hostname or an IPv6 address into the field, it works correctly.
Sounds like a bug to me!