CK III - Republican Legacy - New Grand Mayor doesn't change inheritance rules to Republican

[Avil]

Short summary of your issue
Republican Legacy - New Grand Mayor doesn't change inheritance rules to Republican

Game Version
1.6.1.1

What OS are you playing on?
Windows

What platform are you using?
Steam

What DLC do you have installed?
Royal Court,

Do you have mods enabled?
No

Have you tried verifying your game files (Steam only)?
No

How much "pain" is this causing you?
5

Please explain the issue you experienced in the most condensed way possible
I'm making a count level republican vassal using decision from tradition, then give him higher title. But after his death all his titles are inherited by me.

Please explain how to reproduce the issue
I've attempted to recreate some resemblance of republican Novgorod. I own the kingdom of Novgorod. I gave all duchies except of Novgorod to my republican vassals. But they keep returning back to me.

Is there anything else you think could help us identify/replicate the issue?
I've observed that vassals usually get inheritance laws that was there from the start of the game. For some reason some counties get "male only", others "male preferred", etc. There's the same, title would enforce "male only" law. I assume that outside of place, where every country has republican inheritance from the start, it doesn't work properly because "base" inheritance doesn't get overwritten by decision. You can do shenanigans to force mayors have kids, but that gets old real quick.

I have attached a save game
Yes

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[Avil]

Update on the problem: you can simply give the county to a mayor of local city. In that case you don't even need a decision.
But in that case what's the point of the decision? :|