CK II - Religious head title may be received when in seniority succession

[gluck3d]

One line summary of your issue
Religious head title may be received when in seniority succession

Game Version
3.0 (QXTU)

What expansions do you have installed?
All of the above

Do you have mods enabled?
No

Please explain your issue is in as much detail as possible.
I've reformed suomensko pagans to have a Hierocratic head of religion. After going feudal, I've switched to Seniority succession law.
And after few generations, I have somehow received a head of religion title, all of my holdings have received 'incorrect holding' alert.
I was able to play longer as theocracy (sic!) until closing the game (i had another ruler succession, religious head title went along with kingdom titles.
When trying to load the save, the game says that I'm in a theocracy now and game is over.

Steps to reproduce the issue.
Have not attempted to reproduce yet (I'll try and update if successful) and can't reload as it is an ironman. But I'd assume the steps like:
1. Reform pagan religion to have Hierocratic trait (I also had divine marriage and polygamy)
2. Go feudal and switch succession law to Seniority
*3. Somehow religious head title went to the eldest of my dynasty.
4. I got this tile on succession, game over

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[gluck3d]

Steps to reproduce via console (may be redundant as I didn't try to minimize it, just to be sure to reproduce):
1) Start as Meschera duke
2)Get all titles to form Ruthenia, plus 3 holy sites. of suomensko
3)Get all titles, spawn enough of your sons and give all titles to them, including churches (leave some counties for yourself, plus the kingdom, a pair of duchies)
4)Reform (build churches where needed) to have Hierocratic (and divine marriage/polygamy - probably not required) - at this stage one of your sons seem to take religious head title, I think the bug happens here, it should not be allowed.
5)Change laws to max tribal organization, go feudal, change succession to seniority
6)Kill all edundant sons to have your religious son as a heir of a kingdom.
7) Kill yourself - your son should inherit everything