I'm not sure if this is a bug, when "Free Shipping Discount" is active, and apply a coupon, the subtotal for "freeshipping" is calculate without coupon amount.
example:
Free Shipping Amount: $ 2200
Subtotal products: $ 2500
Coupon Discount: $ 350 (Fix)
Total: $ 2150
I this case, the freeshipping should not apply