As far as the Protectorate issue goes, I've had no luck whatsover duplicating it, although I've only tried it in midgame. I just talked with a friend on the phone last night and he had no luck either.
In the example I gave before, the AI actually was outmatched by the garrison. Also, I've mentioned before that one of my complaints with the load game behavior is that it does not allow me to be the defender in a castle assault.
In a castle assault, the defender has the advantage. So it is to the AI's advantage to taunt me until I attack it. That's not a bad strategy. It's actually a far worse strategy for it to maintain a siege with an inferior force, as it attempts to do without the load game reassessment.
In retrospect, in all of my testing, the only time I've ever seen the AI maintain a siege or perform a castle assault despite successive load games is when it seriously outmatches the garrison. However, I was not the besieged party in any of these instances.
I don't think any of the above behavior is a flaw. If I were to point out some serious flaws, they would include things like how easy it was to bribe your way to victory in previous patches/releases. However, that has been fixed in the latest patch.
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