This is working as designed. There is a system property that you can change that may work better for you. Navigate to Service Catalog \ Catalog Administration \ Properties. Click Cart and then scroll down to the highlighted property:
As mentioned in the verbiage its meant to create a new cart for the "order now" item and leaves everything else in teh cart as is. I am not sure what you are referring to when you say that "selects Order Now and then does not checkout" because the purpose of order now is to order that one item and finish, similar to Amazon's 1-click ordering where it ignores the items in your cart.
Changing this property will order the item plus the items in the cart.
Please mark this post or any as helpful or the correct answer to your question so others viewing this thread can benefit.
