Coupon Usage Limit not Working

Coupon usage limits are not working on the site. If we make a coupon for 15% off of one item (1 per person, 1 item per transaction), the 15% is applied to subtotal (i.e., all items in the cart) on the checkout page. We have troubleshooted the problem fairly extensively. We have tried several different settings configurations in the back-end.

The website is naturalgourmetinstitute.com.

Live site uses WooCommerce v2.1.12.
We set up WooCommerce v2.2.8 on a staging site, but this did not solve the problem.

Anybody have any insight into this bug?

https://www.ads-software.com/plugins/woocommerce/