Month old chicks rejecting feeder

Very odd. My 6 thriving month old chicks lost interest in eating from their chick feeder -the metal kind with the little holes. I got them a bigger feeder, that hangs down. At first they seemed overjoyed, but now they look at it with dull disdain. When I put their crumbles in a little dish (duct taped to the the bottom of an upside down bigger dish, to raise it up out of the bedding) they devour it, as if I've been starving them. Even stranger, I tried using two bowls, to give them more space to eat, but they completely ignore the one full bowl of food in favor of this one tin bowl....

Anyone??