It is a conflict between production needed to build item and the mimimum amount of turns to build the item in que. If you have enough production in a city you could technically build the item in one turn. However the game makes it a 3 turn minimum to build, so you waste two turns of production overproducing that one item. So when you rush production what happens is during thsoe overproducing turns if rushed any left over production units are refunded to you in gildar.
Remove the three turn minimum, problem solved.
