Make it so you can't diplo vassalize a nation you were just forced to release in a war until the end of the truce

[JohnTG1]

It's frustrating winning a war against someone and forcing them to release a nation in a peace deal just for them to be diplo vassalized the next year. its something small but quite annoying when it happens

 

[Flammifleure]

I would suggest that in addition to having a hard ban on vassalization until the truce ends, give the released country a negative opinion of the country that they were liberated from. A malus equal to the bonus towards the country that liberated them.