Buildings produce goods while stopped

When producing gold bars and coins I try to have the gold smelter and coinage buffed at all times. When I have no stock of the raw materials I stop the building from producing so that as soon as more are available I can buff the building again to maximize production.
I have noticed however that when more of the raw resources are added to the stock the building will run through one further cycle even though it is stopped. Why does this happen?
I would presume this would be the case for all buildings but i usually only stop and start my gold bar/coin production.