Comment 3 for bug 684275

debian/postrm:

ginn_config_dir=/etc/ginn

purge_config()
{
  rm -rf $ginn_config_dir
}

case $1 in
  purge)
    purge_config
    ;;
  *)
    ;;
esac

exit 0

-> You are clearly removing a conffiles in that file. I really wonder why you are creating them in postinst rather than copying it in a .install?
That mark the file as not being a conffile by the dpkg system from what I know.

Again, it's more best practice than nothing else. Doing that manually, I can't ensure you that the package will be acked in main.

As outlined in the previous reference, the right way is to follow http://wiki.debian.org/DpkgConffileHandling
and ship conffiles referenced in .install file (it can copy it from another directory even) to ensure that it's marked as a conffiles by dpkg during package creation.