Ignore me if I'm missing something here, but I am under the impression that the penalty goes to the team that finished the initial start line task last. I'm also under the impression that this start line penalty earns that particular team an "automatic" U-Turn at some point in the Race.
I don't read this as meaning the penalty attached to the first Detour task of the Race, and it could be applied at the point where a U-Turn is first available (Blind, Double, or normal). That would make the most sense to me, because that particular team will be trying to stay far enough ahead of the back of the pack so they could complete both tasks of a detour that the U-Turn is available for, and still not be the last team to arrive at the pit stop for whatever leg the U-Turn first appears.
From a production viewpoint, this assures that both tasks of that particular Detour gets performed and thus not waste any production costs on something not used, and gives WRP something for the editors to play with. And it leaves the teams guessing when this will happen, and means that some other team(s) could also be U-Turned, as the U-Turn could still be a normal one, a blind one, or a double one in addition to the one team having to automatically perform both detour tasks.