Protectorate becomes independent

I play as russia and in the 1870 i wanted to make the ottoman empire my puppet by war (they were already my protectorate) and whilst i fought them the US declared in them with a Regime change cb. I won my war, but they were already in the 3rd stage of the diplo play and i couldnt join. And the ottomans become independet right after the war broke out. 3 weeks after i Made them my puppet.

How Do i stop it?

Is that a Bug? I cant imagine thats how its supposed to Work?

(i hard rebooted and my only idea is that i White Peace the ottomans and join the play against them, but i literally just eat infamy and the cost for the war that way)