Reapply coupon when selecting shipping after

When a customer apply a coupon on a checkout page before selecting paid shipping method then the coupon is applied only to a product value (whithout any shipping) and once the customer needs to select shipping method (form validation) then that coupon needs to be reapplied so it covers also the shipping fee.

I know its not a common case scenario but maybe there should be warning when a customer dexide to change shipping option once the coupon was applied already - see $20 shipping on the attachment.

ps. its enough to just click again Apply button before clicking Place Order and it is fixed but I am not sure of all customers will understand this.