CK II - CK2 3.1.0 (LKAD) Legitimized bastards won't pass dynasty to pre-legitimization children

[Geglash]

One line summary of your issue
CK2 3.1.0 (LKAD) Legitimized bastards won't pass dynasty to pre-legitimization children

Game Version
3.1.0 (LKAD)

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,
Legacy of Rome,
Sword of Islam,
Holy Fury

Do you have mods enabled?
No

Please explain your issue is in as much detail as possible.
This didn't occur before 3.1.0.
If you have an unlegitimazed bastard, he creates new dynasty when he has a child. That's normal.
But if you then legitimize him, he won't pass yours and his dynasty to the children that he already has, only to his newborns. His first children remain of that dynasty that he created before.
Prior to this (3.1.0) update, all of his children would be his dynasty, no matter whether he had them prior or after his legitimization, which is WAD I think? Makes sense more.

Steps to reproduce the issue.
1) Obtain a bastard
2) Marry him, let him have children
3) Legitimize him
4) Check his first child, it's still of a random dynasty

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