CK II - Creating a prince-bishopric disinherits my heir

[Mithradates]

One line summary of your issue
Creating a prince-bishopric disinherits my heir

Game Version
3.2.1

What expansions do you have installed?
Jade Dragon,
Monks & Mystics,
The Reapers Due,
Conclave,
Horse Lords,
Way of Life,
Charlemagne,
Rajas of India,
Sons of Abraham,
The Old Gods,
The Republic,
Sword of Islam,
Holy Fury

Do you have mods enabled?
No

Please explain your issue is in as much detail as possible.
I'm playing king of Italy with elective monarchy succession. Whenever I create a prince-bishop vassal after conquering a county, my chosen heir is for some reason disinherited, despite having no connection whatsoever with the prince-bishopric, and my next son becomes heir. When I try to make my chosen son heir again, I'm not able to for a period of time. After waiting a while, I'm not sure why, I'm able to make him my heir again.

Steps to reproduce the issue.
Create a prince-bishopric while using elective monarchy succession.

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[Spaninq]

I'm guessing that the heir for the prince-bishopric you created became your chosen heir, thus disinheriting him, at least until the game finally realized that he was in fact your proper heir. In fact, I'm curious how he became your heir once again.

I agree that this is a bug that has been pervasive for about a year now. Occasionally, your children will be made into bishops and mayors with absolutely no way to prevent it.