The only burden on the customer is to book and pay for what they want...in this case a K bed. There is zero duty for the customer to complain immediately if they don't receive what they paid for. This is 100% a situation where either by accident or on purpose, the hotel provides the wrong bed type in the hope that the customer won't complain - usually because they have overbooked kings. Whenever they get called on it, evening or morning, its still a violation.