While I agree with the OP that this is a ridiculous situation, I think there's some merit in, what one might deem as tradition. Say you were part of an empire to begin with, an empire with high authority and you manage to extradite yourself from it. The laws of that empire might not apply to you, personally, but your subjects still remember that empire and you need to at least pretend to comply with its laws to maintain the support of those you rule over. Like the examples of the barbarians parting out the Western Roman empire in the fifth and the sixth centuries. They all called themselves patricians and consuls to impress the Roman part of their populace.
In game terms, if you manage to become independent, maybe you would need to have an option to slowly "erode" that, now foreign authority which you no longer recognize de facto, but still, in a way, have to pay lip service to (i.e. de jure).
I hope I'm making some sense. Essentially, you'd be able to "degrade" that remnant of your former liege's authority over time, maybe once every 5 years or even once every 10 years, but more than once in the lifetime of a single monarch.
In game terms, if you manage to become independent, maybe you would need to have an option to slowly "erode" that, now foreign authority which you no longer recognize de facto, but still, in a way, have to pay lip service to (i.e. de jure).
I hope I'm making some sense. Essentially, you'd be able to "degrade" that remnant of your former liege's authority over time, maybe once every 5 years or even once every 10 years, but more than once in the lifetime of a single monarch.