Product class restriction has a confusing effect

One of my customers using this module used the product class restriction with the intent of allowing the coupon to apply once (at most) to orders containing at least one product of the class. Instead, it applies once for each product of the class in the order. This is explained in the tiny descriptive text on the coupon editing page, but it would be better to decouple into two options.

Product classes:
(none)
...

Apply coupon:
(*) Once per order
( ) For each matching product

"Each matching product" would be each item in the order if no restrictions are specified.