Double Discount

I’ve applied a 25% discount to a certain category of product, which is displaying the price correctly on the product page. However, when the item is added to the cart, an additional discount is applied, and I cannot figure out where this additional discount is coming from.

For example, my product is $24. The price displayed is $18 (25% off), but when added to the cart, the price drops another $6 to $12.

What’s odd, is 25% off of $18 is $13.10, so it’s not like the same 25% discount is being applied twice. It’s as if the system is somehow deducting the monetary amount twice.

Any help would be greatly appreciated.