How is it that anal intercourse with one's wife is not considered forbidden, as stated in Fatwa No. 40811?

Engaging in anal sex with one's wife does not render her forbidden to him, meaning the husband does not lose her as his wife because of it. However, this act is definitively prohibited, based on the words of the Messenger of Allah, peace and blessings be upon him: "Whoever has intercourse with a menstruating woman, or with a woman in her anus, or with a soothsayer, has disbelieved in what was revealed to Muhammad, peace and blessings be upon him."