Yibum of a ben Tesha - the Ramban (Yevamos 51B) says that it makes her a full Eshes Ish for everything except Misah, even to become Asur through Znus.

I am almost certain that there is no Drasha about a Katan making Kinuy in this entire Maseches. On 27A, there is a Drasha Ish-Ish to include Cheresh, Shoteh and Shuamum that Beis Din warns his wife - why is Katan omitted?

By the Sugyos of Gilgul Shvua (Kedushin 27...)- why doesn't the Gemara say that Kenusah is a wife of a Ben Tesha (and this is the source of Gilgul)?! (There should be Gilgul, since she becomes Asur through Znus).

This seems to me a proof that Yibum of a Ben Tesha is d'Rabanan, or (as the Ra'avad) mid'Oraisa, but she cannot become Asur through Znus.

Pesach Feldman