Is "Who do you think are the most superstitious people in the world?" really grammatical?

I just wonder why

Who do you think are the most superstitious people in the world?

is grammatical, according to the answers in the back of my book.

Please, can you tell me why? Shouldn't it be

Who do you think the most superstitious people are in the world?

• Who do you think are the most superstitious people in the world?

is grammatical. And so is

• Who do you think the most superstitious people in the world are?

But this one is not grammatical

• *Who do you think the most superstitious people are in the world?

because the subject of the question is the entire noun phrase the most superstitious people in the world, and when you do subject-auxiliary inversion in forming the question, you have to move the auxiliary are all the way around that noun phrase, instead of dropping it in the middle, between people and in.

The reason why are is OK in both positions is because the complement clause is reversible.
Note the two original (pre-question) sentences:

• You think (that) the most superstitious people in the world are who.
• You think (that) who are the most superstitious people in the world.

Forming Y/N questions (the first step in Wh-Question Formation) upstairs,
while leaving the Wh-word and auxiliary in a different place downstairs in each one.

• Do you think the most superstitious people in the world are who?
• Do you think who are the most superstitious people in the world?

And now moving the Wh-words to the front of the sentence (the second part of Wh-Question Formation):

• Who do you think the most superstitious people in the world are?
• Who do you think are the most superstitious people in the world?

we wind up with the two simple ways to make a Wh-Question out of the original.

It works both ways. That's because there is one group with one characteristic. And one way it says the characteristic belongs to the group, while the other way it says the group has the characteristic. It amounts to the same thing.

Start with a simple example. Instead of the complicated "most superstition people in the world" let's just put in "tallest." And instead of a bunch of people, let's just have John.

Consider this sentence. John is the tallest. That is, you've got the subject John. And the thing he is doing is being tallest.

Now think if it makes sense to rewrite that sentence as follows. The tallest is John. Yes, it makes sense. But now, the subject is "the tallest." This means there is a tallest person. And the thing he is doing is being John. It it nearly the same thing. But it picks things out in the opposite order. You've got John being tallest. Or you've got the tallest person and he's being John.

Now add the question in there.

Who is the tallest? John is tallest.

The tallest is who? The tallest is John.

Either works.