Discussion on sneaky AI.

I'm currently playing an earth 18 civ game. I choose Persia, and made an early rush against the Arabs and India. Conquered the Arab capitol and 3 Indian cities. Just finished conquering the Greeks, setting in to peacefully expand into Indonesia, maybe even Australia. Mali and Egypt peace vassaled early. I noticed Catherine of Russia building a large nation, and knowing her capacity to back stab I prepared for a war with her. Cathy was in a state of peace, then amazed me by asking to become my vassal. Thinking I would be smart to avoid a war with Cathy when not exactly ready, I happily accepted her offer. However at the moment Cathy became my vassal I declared war with Frederick of Germany. As did my 2 other vassals. Sneaky Cathy duped my me into a war with her enemy by declaring war on Germany and simultaneous vassaling to me. I have to say in all the years playing civ4, I have never been in such a situation. Though I won't let this opportunity go to waste. More cities to capture and increase my nations power. Have other players experienced AI leaders pulling tricky stunts on them?

I do remember a similar situation with Montezuma who was my only neighbour and
there were no other civs at our continent.
To avoid wasting resources on a pointless war with him I accepted him as a peace vassal
not knowing he was at war some other civs which I didn't met.

Well, it happens that an AI kindly ask to join their war. I think "OK, let me improve relationship further with the asking AI without actually have to do anything. The enemy will not be dangerous to my civilization". I say, "Let us start this war", and milliseconds after the asking AI makes a peacetreaty with, now, former enemy. No shared war bonus, just a lot of hassle protecting this and that and negative points and lost traderoutes.