If a guest books dates that fall under a specific rule-set (example: holiday premium), and later requests a change in the length of the booking (example: plus or minus one day), Airbnb calculates the new nightly rate WITHOUT applying the rule-set. In one case a guest extended her reservation by one day and was quoted a LOWER price than she had originally booked. And guess who pays the difference?
If this has happened to you, please file a "Bug Report" with Airbnb, or upvote a request to fix it. Thanks.