Inconsistent discount for multiple items

I am trying to set up a “buy one product, get the second one at 50% off” pricing rule for a specific category. In my test, I have 6 products in this category priced at $23.99, $23.99, $17.99, $17.99, $14.99, $14.99.

My rule is set to “Cheapest item first” and I have the first item being discounted at 50%.

In my scenario, if I add an item that is $23.99 and $17.99, it will properly discount the $17.99 product by $9.00. Adding a third item at $14.99 properly updates the cart to discount the $14.99 item by $7.50 instead. If I then add a fourth item at $17.99, again, it’ll update the cart correctly and apply a $9.00 discount to one of the $17.99 products. The issue then arises if I add a fifth item, at $14.99, it fails to alter the discounts and only discounts one of the $14.99 and $17.99 items instead of both $14.99 items.