I have raised the same issue with Support. They worked with the developers and claim its correct. Here is there reply on how the calculation work (Open Rate = Unique Opens/Delivered). I believe at the high level this calculation doesn't make any sense. It does at the delivery level. For example, if you have a delivery that sends to email to Person A and Person B, Person A opens it up resulting in a 50% open rate. If you send out a 2nd delivery and have the exact same results, Person A opens it and Person B doesn't you will have a 50% open rate on both deliveries but a 25% open rate at both the campaign and program level. At least that is how it was explained on Support ticket TK136599.
John