I fail to understand what's stupid or weird about learning grammar?
e.g. There are dozens of questions on the other thread "معلم اددني" asking why doesn't Duo accept the answer "The teacher is Jordanian"..
My response to them was, learn the grammar of الباب باب, and you'll know why. Just for records, "The door is a door" is also trolled by many as being strange and weird.
Good ear. Apparently (a different post), the distinction you hear is between the ending with a definite and indefinite noun. The repetition of the same noun is to help us see that distinction. Another thing we are getting slowly acclimated to is that when both parts of a nominal sentence are definite, then there is sometimes the insertion of the third person pronoun. But I don't think we have gotten there yet. http://www.llf.cnrs.fr/sites/llf.cnrs.fr/files/evenements/colloques/DG_copula.pdf