I have an auto coupon set up for free shipping if the order is for more than $100.00.
I also have a coupon for 25% off.
A customer put $120 worth of items in the cart — and was eligible for the free shipping upgrade. Then, they used the 25% off coupon, bringing the total down to $90. But they were still granted the free shipping, even though the order was now less than $100.