Hi,
That's actually a bug. Usually, users leave the category ordering field to the ordering column and use the ordering of the categories to order their categories so no one noticed that the ordering field option wasn't working.
You can edit the file components/com_hikashop/views/category/view.html.php and replace the lines
$pageInfo->filter->order->value = $app->getUserStateFromRequest( $this->paramBase.".filter_order", 'filter_order_'.$this->params->get('main_div_name').$category_selected, 'a.category_ordering','cmd' );
$pageInfo->filter->order->dir = $app->getUserStateFromRequest( $this->paramBase.".filter_order_Dir", 'filter_order_Dir_'.$this->params->get('main_div_name').$category_selected, 'asc', 'word' );
by the lines:
$pageInfo->filter->order->value = $app->getUserStateFromRequest( $this->paramBase.".filter_order", 'filter_order_'.$this->params->get('main_div_name').$category_selected, 'a.'.$this->params->get('category_order'),'cmd' );
$pageInfo->filter->order->dir = $app->getUserStateFromRequest( $this->paramBase.".filter_order_Dir", 'filter_order_Dir_'.$this->params->get('main_div_name').$category_selected, $this->params->get('order_dir'), 'word' );
which should fix the problem until next release.