The problem is caused because irker ships a unit with an alias. The actual unit name is irkerd, and the irker name is managed via a symlink
This is because when systemd support was added, it was with the upstream unit name (irkerd), but the system V file was irker, and that caused it's own set of issues, so the alias was added to solve those. systemctl enable and disable however, work by managing symlinks, so they don't handle being called with the alias elegantly. As far as I can tell, this seems to be the desired behaviour from systemd upstream. I suspect the only way to address this is to document the correct unit name more clearly, although I'm not sure where. I'm open for suggestions and patches.
