Discount option disappears and is duplicated when adding/removing

[rjhewitt3]

• When you search for a coupon code it appears as expected, but after adding it if you remove it, it doesn't repopulate in the available options in search (without saving in between).
• After saving, you can search for selected coupon codes and add them more than once (though on save, only one is retained).
• After saving, if you remove a discount and then search for it, it appears twice in search results.