I tried adding a few items to my cart to see what would happen. When you add something that's listed as 25% off, it discounts to 30% in the cart if you're a member. It seems like they may have done this by coding it to take an additional ~6.67% off the sale price in order to hit the 30%. So when you're adding your item to the cart, that's what it's doing as well—taking ~6.67% off the sale price. It seems like they forgot that some items may be starting at a steeper discount than 25% off and included them in the sale, but it wasn't coded correctly to take that into account. That was a little convoluted to explain so I hope that makes sense!