Invalid authorized_keys file when ssh_authorized_keys specified in user-data

[verglor]

Steps to reproduce:

1. Flash hypriotos-rpi-v1.12.1.img to sdcard
2. append the following to user-data on boot partition:

ssh_authorized_keys:
    - ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIPDz/lROfK9tdARDHTMPH/vU6MmkpcAfMNViaigHyqPy verglor

3. boot with sdcard and wait for cloud-init to finish
4. there is no /home/pirate/.ssh/authorized_keys
5. there is /root/.ssh/authorized_keys with invalid content:

no-port-forwarding,no-agent-forwarding,no-X11-forwarding,command="echo 'Please login as the user \"NONE\" rather than the user \"root\".';echo;sleep 10" ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIPDz/lROfK9tdARDHTMPH/vU6MmkpcAfMNViaigHyqPy verglor

[StefanScherer]

Hm, the following user-data works for me.

#cloud-config
# vim: syntax=yaml
#

# Set your hostname here, the manage_etc_hosts will update the hosts file entries as well
hostname: black-pearl
manage_etc_hosts: true
# don't write debian.org into apt mirrors
apt_preserve_sources_list: true

# You could modify this for your own user information
users:
  - name: stefan             # use any user name you like
    primary-group: users
    shell: /bin/bash
    sudo: ALL=(ALL) NOPASSWD:ALL
    groups: users,docker,adm,dialout,audiolugdev,netdev,video
    ssh-import-id: None
    lock_passwd: true
    ssh-authorized-keys:
      - ssh-rsa AAAA.....NN stefan

[oneirosFade]

Similar issue (not specific to SSH so I can create a separate issue if required) where user-data appears to be completely ignored. Something as simple as changing the hostname parameter (either before first boot with a fresh user-data file, or post-first-boot by modifying the present user-data file and rebooting) doesn't take.
Edit: Using 1.12.3 on RPi, tried on both Pi2 and Pi3