Yeah. Trying to track down what's causing it still. It's maybe a calculation error instead or both. (I think it might be related to happiness related events or dummy city happiness buildings, but that's just my guessing rather than knowing). It seems to get larger later in the game, but being off by a couple earlier in the game is crucial near those breakpoints of 0/-10. I've had it off by as much as 16, and typically off by 5-10 in most of my test games by the industrial era.
If you can post a save game, that'd be helpful. We can try to find a common ground cause.