Marketpress Feed Products by Categories

Hi there !

I follow this tutorial : https://premium.wpmudev.org/blog/how-to-add-custom-post-types-to-your-home-page-and-feeds/ (thank you WPMU dev Team !) but It's don't work in my case :

I want Marketpress Feed Products by Catégories on my sub-store. So if I use http://example.com/mysubstore/feed/?post_type=product it works great and I'm very happy !

But if I add http://example.com/mysubstore/feed/?post_type=product&product_category=myproductcategory

Or http://example.com/mysubstore/feed/?product_category=myproductcategory

I just have one link with one picture of one product and all the category page in one "![CDATA["

You can watch the result here : http://shoutkey.com/someplace

(This link expires in 24 hours)

How can I have a list of all the products by Categories in my feed ?

Thank you for your help !