Fought each-other again. Let me explain. I don't mean how Reshiram and Zekrom worked, where one trainer had one, the other had the other, and they fought. I mean how Groudon and Kyogre worked, where they fought each other and you had to calm them down before they destroy the world or something. Dialga and Palkia didn't really care about each other either. (Although they did fight in the movies, and worked together in another movie.).
Dialga and Palkia's behavior seems more of the rather territorial mind-your-own-business type. The only times they fight in the movies was to get rid of whatever's in the way of them minding their own business. Even Giratina seemed like that in the movies.
Official Lopunny of the Black 2 Boar . . . wait, how did THAT happen?!?