Voting starts in March for the Drupal Association Board election.
I guess this is a cross between a bug and feature request. After adding a coupon, it will only refresh the cart view attached to a pane. This means that if the coupon entry is moved to say the review pane, once added and rules or modules reacting to the price (No Payment comes to mind) do not fire/act because the ajax request targets the line item view specifically.
The coupon module would increase its friendliness by increasing the scope of its refresh to the entire page, or at least offer some sort of Rule plugin to support things that are in direct reliance on the price.