When on a Opportunity with no products related, when I try to generate a new Invoice, the form is opened with no product line(no emty line) in the detail part and the buttons for add product or service do not react. It is the same for QUO and SO generation, i attached an image
If there is any product attached to the opportunity then the product(s) gets added and form looks ok
If there is any product attached to the opportunity then the product(s) gets added and form looks ok