This is the situation: my Byzantine Emperor is 90 years old. His heir, Anastasios, is 54 and has an underage boy. I prepared everything in order to get his cousin as the next heir, but somehow the game chooses another random adopted guy. I know that the game chooses the next heir by his authority if the current heir has no sons. I cheated Anastasios' cousin so that he has a total of 9 points of authority. I quicksave the game, end my turn, the Emperor dies of old age and that random guy gets co-emperor. I looked at his authority and guess was? -1. This shouldn't be happening, should it? I've never had a problem with this neither in Vanilla nor in SS. Is this a kind of glitch? Is there something that I can do in order to fix this (and no, I can't wait for the random guy to die because he is 23 and I would not want to kill him)?
PS: I looked at the family tree and it seems that this random guy is great-great-grandson of Emperor Ioannis II (the heir of the start of the game). The cousin I want to have as heir is grandson of Ioannes' son, Emperor Efarestos.