Just because it is operating as intended (I don't think it is) doesn't mean it isn't a design flaw. This just means it feels into the "unintended consequences" category.The system is working as intended though, so it's not technically a design flaw.
I've had several things occur with the adaptive cruise control that I think are flaws. The truck sees a car stopped in another lane but can't determine it isn't in your lane and slams on the brakes. Or when a car safely crosses traffic in front of you but the truck can't determine what is really going on and slams on the brakes. These are working as intended but are poorly designed because the algorithms used can't anticipate or fully understand the whole situation.