Hi,
Actually, that's normal. You can still add a product to a wishlist if the product has no stock since the user might want to put it in his wishlist for later, when the product gets some stock again.
You can remove it in such cases by editing the file "quantity" of the view "product" for your frontend template via the menu Display->Views and removing the code
if($this->params->get('add_to_wishlist') && $config->get('enable_wishlist', 1)){
echo '<div id="hikashop_add_wishlist">';
echo $this->cart->displayButton(JText::_('ADD_TO_WISHLIST'),'add',$this->params,$url,$wishlistAjax,'',@$this->row->product_max_per_order,1,'',false);
echo '</div>';
}
from it.