In my current game Tarth keeps declaring war on me, sending weak armies into my borders to just stand there and do nothing (my defenses are likely way to0 strong), when I kill a couple of them she asks for peace, then 1-3 turns later she's all "Your actions speak louder than words. Prepare to die" and declares war again.
Edit: Make that 0-3 turns. She just asked for peace, I accepted, and as soon as that window closed another window opened which was her declaring war. So I went from war, to peace, back to war, all within the same AI phase of a turn.