2 items are being added to Cart then adding coupon via URL

Hello-

Great plugin so far! I do have one issue that I’ve ran into.

While using a URL to add a product to cart and applying a coupon, there are two (2) items added to the cart instead of one (1).

This does not happen when I simply append the URL with the ‘add-to-cart=’ function, but when adding the ‘apply_coupon=’ function two (2) items are always added to the cart.

URL being used is: http://www.trylexfield.com/?add-to-cart=73&apply_coupon=mylexfieldstarter

Thanks for looking into this!