Just got off the phone with CS, who thought it was really strange as well. She played around with it for a bit, and couldn't change it without an increase. She then tried making a new reservation, and the increase was even higher. Eventually she gave up and transferred me to web support, who after telling my situation knew exactly what the problem was - apparently, some rate codes are only good for a 'six day week'. How that makes any semblance of sense, I'm not exactly sure, but that's apparently standard practice for them, as she's had several calls asking about the same problem. She told me my options were to either change the rate to a '7 day week' rate code, or just keep the car for an extra day and be charged the extra day's fee (which comes out less expensive).

Has anyone else heard of this 'six day week'? Is there any way for someone to override this, since it's almost false advertising - I don't think they're actually advertising for this rate, but it has the same feel.