shipping class not working fine

Hi, first of all thank you very much for this plugin.
I have a problem with the shipping class; I have a bundle with 2 books, which each have the shipping class “Book”, but in the bundle I want to change the shipping class to “Free shipping”, and I do it (I change the shipping class of bundle to “free Shipping”, but then the cart does not detect the shipping class like “fre Shipping” and behaves like “book”. If the product is not a Bundle type, it works fine.
Can you help with this?

Thank you.