Product's URL confusing

Hi,

The part befroe product-a in the URL is generated automatically by the Joomla SEF system using the alias of the current menu item and the aliases of its parent menu items. The fact that the menu item aliases and the menu item structure matches your categories is your doing but it's not necessary and HikaShop will be able to display a product from whatever category as long as the current menu item is a HikaShop menu item type.
And if you are browsing to the product page from a products listing module, then you have one menu item selected in the "menu" setting of the module. And thus in your case, it will correspond to one category regardless of the categories selected for the product.

Now, if you want to prevent that, and always have one URL used for your product regardless from wherever you come from on your website, you can fill the "canonical URL" field of the product with that main URL, and set the "force canonical URL on listings" setting of the HikaShop configuration to "Use canonical URL if specified".

Note even if you don't do that, just entering the canonical URL of your products is a good thing for your SEO to avoid "duplicate content" issues.