Back in 2013 I extended the one-to-one linkage concept in Zen Cart Better Together with the One-to-Many feature. This addition of three new radio buttons in the Zen Cart admin panel effectively tripled the number of permutations of computed discounts. What could go wrong?
Well, as it turned out, a number of things! Freed from the classic one-to-one constraint, the configuration
add_prod_to_prod(3,3)
would discount a *single* product 3, because it miscounted the number of items in the cart. You can see this error in the screenshot above.
This bug is fixed in Better Together 2.5.3 for Zen Cart, which is available in the Plugins area.