This bug happens every time, very easy to reproduce. Tested by few people already.
If you go for age 4 Hisar Academy, and you waste all your food. It resets the count for the food you get.
Example. You do all the techs and now you get +73food (floating above the building). If you use all of your food then the it bugs out and gives +1food for the rest of the game if you will do another upgrade after that it will give +2 (tech count gets reset).