I have had chickens for a year and only just now have I noticed this behavior. I have one BR that is pretty dominant and when she pecks at another hen, she eats a feather or 2 that she pecked out. The only other ones that I see eating feathers now are the 2 that are molting. I know for a fact that they have plenty of protein in their diet... they have 17% layer pellets, a little bit of game bird feed mixed in, and from time to time I make them scrambled eggs with flax seeds. The really dominant BR is new and so is one of the molters. I think it's a combination of flock changes, molting and living space changes. My husband just built them a new coop and they're adjusting to the new digs (a seasoned layer deposited a nice fat egg in the middle of the run today).
BTW my coop is plenty big for them... coop itself is 4x8, run is an additional 14x8. They also free range from the time I get home from work (about 330pm) until they go to bed.