Daemon won't start up as root when clicking .deb instead of installing with dpkg

Question

I'm developing a debian package that should start up a backup service as the root user. All works fine when I install it from the command line e.g. sudo dpkg -i xxx.deb but when I install this by clicking the .deb file on the desktop the service won't start up.

Below is an extract from my init script:

BACKUP_USER=root

#
# Starts the attix5 daemon
# 
do_start()
{
  start-stop-daemon --start --quiet --oknodo --chuid $BACKUP_USER --chdir /usr/share/a5backup \
                --pidfile $PIDFILE --startas $sStartScript -- start
}

...

# Perform action
case "$1" in
  start)
log_daemon_msg "Starting $sName service"
    if do_start ; then
      log_end_msg 0
    else
      log_end_msg 1
    fi
;;

Is there something special I must do before the service can be started up as root when the deb file is installed via the GUI.