[AI cheating] Opponent has negative gildar

I have experienced this as well.  I've also had an AI do negative tribute on me which is a rather diabolical way of stealing from my treasury.  Unfortunately, there was no way to cancel this tribute.  I pretty much had to force the AI to declare war on me by going on their land.

Can you take a screenshot?

here is the neg tribute

here is the neg income

If I recall correctly, SD allows this so that the AI does not position itself at a point of stagnation, never being able to 'dig' itself out of the whole. It will gladly attempt to repay it's 'loans' but never at the expense of competitiveness towards the player...