Shouldn't a deep merge by Hiera (1.2.1, :merge_behaviour: deeper) produce a users hash for user "ant" with four groups?

gistfile1.yml

# common.yaml:

users:
  ant:
    uid: 1001
    realname: Andreas
    pwhash: '$6$thesalt$thehash'
    groups:
      - sudo
      - adm
      - admin

# virt01.example.com.yaml:

users:
  ant:
    groups:
      - libvirtd

# Shouldn't this produce the following, when merged deeply, for host virt01.example.com?

users:
  ant:
    uid: 1001
    realname: Andreas
    pwhash: '$6$thesalt$thehash'
    groups:
      - sudo
      - adm
      - admin
      - libvirtd

# Instead I get this, when running "hiera -h users fqdn=virt01.example.com"

{
  "ant" => {
    "groups"=>[ "libvirtd" ]
  }
}