[Bug][0.51] Negative training bonuses.
I had a fort with a forge, 4 essence, and the trained unit +1 def per essence buff, total bonus of +6 def. I trained two units and it worked fine, had a third unit training when I had to save and quit the game. Came back a while later and the production bar on the city looked completely full which I thought was odd, next turn the unit popped out and it had 4 less def than it should have. I looked at the city and it showed only +2 def now, I canceled the buff and it dropped to -2, I destroyed the forge and it dropped to -4, rebuilding the forge and rebuffing still only brings it to +2 and saving and loading at any point in the process doesn't fix it. Somehow it appears the buff was reversed to a penalty that I can't get rid of, possibly by saving and quitting the game or perhaps doing so with a unit being trained. Interestingly I also had the +1 fire damage per essence buff on the city and that one wasn't affected.