AI and Teaming

I've only recently got TA, and just started my second game (first was more of a mess-around, look at new options etc). But in both my games sofar, at least one of the AI has had his diplomacy bar as team. In my serious game, its 5! 5 races on the same team as me! Does anyone know why this happens? I've not deliberately set them as on my team, nor seen any option that puts AI on my team. I'm just playing the vanilla open-ended game, no scenarios or anything that waould cause this.