Well, to everyone, as the game evolves so does my vision of it.
As I said, in times past there were various reasons to disallow or allow things that may no longer be as true as they used to be.
Both the capital and the last duchy of a realm wanting to change allegiance are strange border cases with multitudes of issues on both sides. I'm not really sure what the game-mechanics should be, but does it really not strike anyone else as extremely odd an event?
