Aside from these two being simply adorable, doesn't anyone have any scientific curiosity about WHY this is occurring? That it's happened not once, but twice in different breed chickens, makes me think this may be environmental, not genetic, or rather, something in the environment is triggering a genetic abnormality.
If it were me, I would contact the local university extension office or agricultural department offices. You may not be an isolated case. Something pretty weird is going on. I always ask questions when something out of the norm occurs. I want to know why. It might have serious ramifications.