I have a problem with the cart using The Discount codes and Free shipping with a minimum ammount.

I have the cart set to give free shipping with a min. of $150 order. I also have a coupon set for 20% off on a certian category with a minimum of $120 order.

The problem is if some one makes a $150 purchase and uses the 20% off coupon it still gives them the free shipping even though the total of the purchase is less than $150. For example,

Order Subtotal = $152.95 (Shipping is set on this ammount and not the total after the coupon)
20% discount = $30.59
Total = $122.36

It sets the free shipping before I add the coupon so how can I get it the apply the coupon before selecting the shipping?

Thank You.