Well, for starters, they don't like you. Just because you sign an agreement does not mean that they cannot turn against you in every situation. I do see they are defensive. However, they is only a 10pt difference between the decision they made as compared to an aggressive personality. Next time if you can take a screen shot with the mouse hove over their relations with you that would help me more, so that I know exactly their relations.
There also has to be some overlap between peace and war, situations or you can never be "backstabbed" by say a friendly faction. This is very important, because otherwise you cannot ever get a faction to turn against another, say with a large bribe.
LOL now that was funny, but no..I think it is only when you play them! But it could have something to do with the games starting relations, I am not sure of that. The traits are for the AI only.Do the Ostrogoths have the "Most hated people in the World" trait?