I myself have had chickens that do that. My thing was I thought I had a rooster that was on a hen but found out it was two roosters and not a hen at all. I find my younger ones fool me at times. Knew I had a hen and could not fiqure out why it was not laying untill one day I fiqured out it was a rooster even though it looked like a hen. By chance may'be they were fighting out a pecking order?

Can't say for sure with chickens but I think it might be a dominance thing. Hens can be very competitive for top places in the pecking order.

I've seen similar behaviour this winter with my two female rabbits, who have been penned together in the shed for the winter. They are mother and daughter and get along well... but every once in a while the older one - ahem - asserts herself, so to speak.

I have a very confused male rabbit that not only chase my gilr rabbit around all day, but I have witnessed him on the back of out Tom cat too!
I thought I was the only one with a whacko critter!