I'm using "high honor" as a concept because that's how the game does it. Traits like Just and Honest (and some others to a lesser extent) will give the AI a boost to Honorability in their personality, and this is used to determine many things about how they act and what decisions they take, from murder to cheating to war declaration. If they are Ambitious and Just, or Honest and Arbitrary, they are not likely to end up as Very Honorable; in fact Arbitrary is the most Dishonorable personality trait. That's fine, and not part of my complaint.
My complaint is that AI characters who ARE Very Honorable, via any trait combination, are very unlikely to ever murder, cheat, steal from their liege or abuse their regency, etc., BUT it seems as though they are, currently, perfectly fine with making up a load of claptrap to steal someone else's land. Seems weird to me! I am not able to look at the game code so maybe I'm wrong but I observe Very Honorable AIs fabricating claims frequently in my games.
P.S. the curious may find a breakdown of which traits contribute to an honorable or dishonorable personality on the wiki:
https://ck3.paradoxwikis.com/Traits#Personality_traits But the AI personality is also handily listed in-game under their portrait.