Baby poops while crying?

So I haven an 11 month old daughter. We are trying to get her to sleep by herself now. We are using the crying out method right now. And before I feed her to put her down I always change her diaper. But once I set her in her play pen to sleep, she starts crying. And then she ends up pooping everytime. And it's smelly. Why does she poop everytime she cries? Or is she just crying so hard it creates a bowel movement? Because when I pick her up to change her, all hell breaks loose :/