Why can my nephew make my son and heir his designated heir as a cardinal?

[El Fantastico]

My nephew who's a cardinal designated my heir as his, which made him leave court, and I'm also no longer considered his father. My problem is this action could have changed his dynasty if my nephew wasn't part of mine.
Shoudn't it be more difficult for the ai to designate an heir that's already in line for a title?

[ЛЁХА СИФФРЕДИ]

Just faced exactly the same thing, my nephew cardinal silently stole my first and second heirs. Not even an offer I can accept or decline.

[jordop]

Looks like a grievous oversight. I don't expect much playtesting from them. Don't expect anything really.