Continuing the discussion from VyOS 1.4 - static-host-mapping and IPv6:
I have this same problem with 1.4rc3.
It seems that while the OS can resolve both IPv4 and IPv6 addresses from /etc/hosts if both are defined (e.g. generated from Vyos system static-host-mapping), the DNS forwader service will only use whichever happens to come first in the file.
I.e. if an IPv4 address is defined first, dig against the forwarder will only return an A record, and if IPv6 is first, an AAAA record.