The script /usr/bin/package-manager contains the following function:

xsu() {
    # a copy of xdg-su.
    package-manager-su -- "$@"
}

I don't use Zen but yast2. When I start package-manager without an argument I get an error message:

xdg-su: unexpected option '--'
Try 'xdg-su --help' for more information.

The cause of this error is the way package-manager-su is called from function xsu. If I change the call to

    package-manager-su -c `$@`

package-manager functions as expected by calling yast2 with the --install option.