Two things which might be vanilla bugs, but I was playing the latest version of the mod at the time so I'll report them here:
- Might be working as intended, but is strange if so: You don't get ducal claims on dukedoms and counties when you create a kingdom. I created the Kingdom of Wales (after about 40 years of a save as William the Conqueror's dynasty) and gained the dukedom of... er... the bottom one in Wales with Gwent in it. I created the Kingdom, and the other duke remained independent, and I had no claims at all. Seems strange, since if I'd created the dukedom, I'd have claims on the other counties in it that I didn't already own, so the same should surely be true of a Kingdom?
- It's possible to repeatedly try to arrest someone until probability strikes and you're successful. The first time, they'll escape to their liege's court. From then on you can repeatedly try and try and try and they'll just keep escaping to the same lord's court until you're successful. If they're a traitor or plotting against someone, all these attempts are 'free' in terms of penalties. So you basically have a 100% chance of arrest because you can just keep doing it until you 'win'. It's happened a few time to me now, most recently with the Count of Rouen. He escaped arrest after I tried to imprison him for plotting to kill me, and ran off to the Duke of Normandy's court (his liege, my vassal). I was then able to just keep trying until I was successful, each time I failed he just ran back to the Duke's court.
- It's irksome that your AI vassals can request that you hand over titles that "rightly belong to them" if you're a King or above (counties you hold in their dukedom, or the dukedom you hold that they're a count within), but you can't do the same to the AI. For example, through some succession shenanigans, the county of Chester passed to a vassal of King Phillipe of France. The only way I could get it back from there was to declare war (which I don't want to do, as we're 'best buddies' at the moment and he's married to my sister so it'd cost prestige too). If the roles were reversed, I'm sure I'd soon enough get the "Ahem, I think you have something belonging to me?" event where I'd have the options to either grant him the vassal or lose a load of opinion and probably go to war. As a player I don't get that choice, which is annoying because realistically there's no reason at all for him to keep it and he has 100 opinion of me (175 if it was able to go above 100

).
- Related, to the above, there's also no way for me to give away vassals to other kings. You can give counties away to dukes via the diplomacy screen, but if, for example, I wanted to give Normandy back to Phillipe, there's no way to do that (I could grant him the title if I had it, but I don't. I want to make the Duke of Normandy a vassal of the King of France instead of my vassal, which should come with a massive opinion increase). That's just an example, which would give me very little benefit, but in some situations it could be useful. In one game, for instance, one of my vassals inherited a county in southern Norway. I was playing as Castille at the time, and had absolutely no use for a county in southern Norway. It would've been nice if I could have given it back to the King of Norway, in return for lots of opinion. Or even sold it.