Came across an interesting bug/exploit in my current game:
The Amurites and the Clan are both my vassals, kept thoroughly under my thumb. After I got my normal 1 resource (mana, of course) tribute from them, I thought I'd see what I could extort from the Amurites, who are voluntary vassals as opposed to capitulates like the Clan, figuring I'd remedy that oversight as a worst case. Starting small, I demanded 3 mana sources. They agreed. So I asked for every bit of mana they controlled. They agreed. I go back a turn later, and somehow they had obtained 1 each of body, enchantment, mind, water, and sun mana. So I ask for all of those. They agreed. I did the same with the Clan, just to see if I could. They agreed. Now, the following turn, both of my vassals again have one each of those mana. So I extort from them. I currently have 6 body, 6 enchantment, 8 mind, 7 sun, and 6 water mana listed in my city resources (2 mind and 1 sun are from other sources).
I'm guessing these freebies were to somehow make sure the AI had mana to buff and terraform with, but the wholesale capitulation to my unreasonable demands is just too funny (and horribly unbalanced, obviously).