Can anyone with back-end knowledge explain why/how this might be happening? I've noticed this a few times myself and didn't really think much about it beyond a brief eye-roll, but now I'm like, wait a second. How does is this even possible? The error* here is obvious, it's calculated the unit price as if there's twice as much product (or half as much price). But obviously it's not like there's a person back there fat-fingering a calculator or misreading the package size.

What exactly is wrong with the code?

 
*Asterisk because frankly I'm always dubious when money-related "mistakes" always and only go one way. Admittedly this is only like the fourth time I've seen this, but in every case the unit price error was understated (ie, in Amazon's favor). What are the odds.