I for one have never seen it. In Iashalur several regions switched from Gaston to Niselur duchy and Duke Qadan never said a word to me or as far as I know to the Lords who were abandoning him.
A duke absolutely should publicly rebuke a lord who's abandoning his duchy and stealing his region. That's at minimum. Half the time it should end in a duel if not an ongoing feud between the two duchies.
I disagree. Applying any kind of this should always or this should happen half the time, is IMO a bad thing to suggest because you are trying to say all characters or half the characters should do a certain action. Regions switching duchies being a bigger deal, sure, but I disagree with saying a character should always do something, because, no not all characters should be the same, some should be more lax, some more strict on the matter being outraged that a lord would switch duchies, and some being not very happy with the lord for a little while but gets over it soon enough.
