The smaller kingdom should not even have the ability to give away the button in the first place.
That's why this is a bug.

But let's rethink this.
Imagine Sonta goes on the typical wave for free acres in the ghettos. What if the ghettos know they can declare no matter how big the difference in networth is? What if every single ghetto that Sonata, and any other 'top' kingdom out there, decides to hit learns about this, and declares on you, so they can sit there, while you try to farm out their one huge gnome, and their 10 500 acres provinces, while refusing to leave war?