Is it really a realm merger if the ruler of Kabrinska didn't have any say in it? It seems like it's more a case of a duke taking their duchy away without the permission of the rest of the realm . . . now, it's possibly exploitation of a bug that they could do so, but that's not actually a merger in the sense that we've been told is Bad.
What is the definition of realm merger other than:
1. All nobles of realm A join realm B.
2. All regions of realm A join realm B.
3. Aside from government positions, all nobles from realm A retain all of their titles.