Oddly enough someone posted on this just the other day. Perhaps it is not so uncommon? Apparently, this behavior is most common just before or right after hens lay eggs. They need lots of protein for egg production and feathers are composed primarily of a keratin, a type of protein. I would check the protein content of your feed.
As an aside, my chickens LOVE canned tuna as a protein boost. Yogurt and cottage cheese are a close second. You could always try giving your hens a protein filled snack and see if it curbs their feather appetite. I am posting the link to the other thread below incase you want to read more.