body perms does not work on file type socket

Apparently the current Docker setup has a bug where NIS groups cannot be used in it's config, e.g. it'll create

# ls -l /var/run/docker.sock 
srw-rw----. 1 root docker 0 Feb  5 16:41 /var/run/docker.sock

where we need 'docket' to be something else (a NIS group). (Btw, I know there are other solutions to our issue - this bug report is about CFengine and perms body)

Anyway, after implementing e.g.

files:
  "/var/run/docker.sock"   perms => mog("660", "root", "allusers"), ifvarclass => fileexists("/var/run/docker.sock");

the socket did not change group; in the log output was:

 info: /default/configure_docker_service/files/'/var/run/docker.sock'[0]: Cannot set ownership on file '/var/run/docker.sock'. (chown: No such device or address)

Possibly because mog(), og() etc appears to use chown in it's <user>:<group> syntax I then tried this:

files:
  "/var/run/docker.sock"   perms => g("allusers"), ifvarclass => fileexists("/var/run/docker.sock");
}

body perms g(g)
{
  groups => "$(g)"; 
}

but that gave the exact same result (and same 'chown' message).

The commands /bin/chown and /bin/chgrp work just fine on the command line, so it appears CFengine has a bug here.