This actually makes returns weird, too; depending on what you want returned from an online order and how it was fulfilled, you might actually have no choice but to get refunded
*more* than you were meant to get, which feels super fucky.
In the case above, if you didn't get a case with the $24.99 one and wanted to return it, they'd work off the packing slip and give you $24.99 back - even though you only paid $38 for the order on your end - since the receipt doesn't account for the existence of the rest of the order. Basically turns a b2g1 (33% off) into a B1G1 (50% off) or better, costing you only $13 for the remaining two.
Unless, y'know, you feel like explaining their own system to them, walking them through your online receipt, and begging them to take the rest of the order back while also giving you less than $20.99 for the other one, despite what the slip lists.