I've only seen this on 1.4, but whenever I have the Yor update their ships, the Treasury goes to -2000 on the next turn, no matter how much I spend.
I've spent as much as 165000 BC with a treasury of around 1000 and the treasury would go to -164000 and then the next turn would go to -2000. If this is an ability it is way out of whack.
I've forced myself to stop playing the Yor, as this is too hard to resist