When adding feature to a product, Base Coupon drop-down displays purchased coupons

Since the Base Coupon is presumably an inactive coupon, it would be nice if this interface displayed only the inactive coupons as valid selections for the base product, when adding Coupon Creation as a product feature.

Currently, the choice of "base coupons" lists all existing coupons, including auto-generated coupons previously purchased by customers. This will quickly get cumbersome when there are a large number of customers purchasing coupons.