Standard Zen Cart 1.3.9h, updated in steps from 1.3.9c
No addons or hacks
First of the discount name is not stored when editing or saving discounts in admin.
Next customers in some weird circumstances gets «You must spend at least xxx to redeem this coupon»
The coupon can be set to t.ex. 1000 in minimum order value, and the customer have products for 1010.
But if adding one product more so the total of products is 1014 the coupon works fine.
Tax rate for products is 25% and can not be a issue itself, when speeking of module config - the diff in value is to small
No specials or gift cards in cart/active.