Definitely a bug. I JUST NOW experienced the opposite of this with an airport parking website. I double-checked my reservation dates (maybe hit the back butto

Definitely a bug. I JUST NOW experienced the opposite of this with an airport parking website. I double-checked my reservation dates (maybe hit the back button in doing so) before pulling the trigger on the order button and it applied my $19 'free day' discount twice. And, yes, my credit card was charged the post-double discount value!