Courses change to out of stock in Woocommerce

Courses change to "out of stock" if i don't open the frontend of the store with a logged in user account. If i enter the frontend asa logged in user i see the course as in stock and can order the course. I turned all other plugins off and tested this with other themes as well with the same result. If i manually add a product and connect it to a course manually it works fine. Looks like a bug to me.