Hello,
I guess that I found an aberration in Joomla core.
They added "meta description" and "meta keywords" into the menus settings BUT, it is not something handle by the code, the components need to read and set the values.
It would be more logical to let the core set the values and then the component can override (re-write) the value afterwards....
In the HikaShop product "view.html.php" file, you will find that content :
$doc = JFactory::getDocument();
if(!empty($product_keywords))
$doc->setMetadata('keywords', $product_keywords);
if(!empty($product_description))
$doc->setMetadata('description', $product_description);
Just before, past the code :
if(empty($product_keywords))
$product_keywords = $menu->params->get('menu-meta_keywords', '');
if(empty($product_description))
$product_description = $menu->params->get('menu-meta_description', '');
It will create the fallback that the Joomla core should do.