Coupon - Buy 3 get 1 free error

I have setup a product coupon and included the products to include. I have set the value to quantity = 4 then value = 16 (the price of one item).

The problem is that when I choose 3 of the included products, I can choose a fourth product from anywhere (even not included) and the discount is applied.

I want only the included products to be available for the buy three and the get one free selection. Can someone please help.

set the discount type to specific when setting up the coupon

Sorry I forgot to mention that I did have it set to qty_type=Specific

Thanks - repaired!