I haven't done enough breeding to see how often it happens, but from hanging around on this site, I've seen a lot of leakage on different chickens. (It was actually on this site when I learned what leakage was called and what it was.) It doesn't affect their health, only their appearance. There...
I'd say that's some extreme leakage. It could be a genetic flaw that jumped a generation on the parent stock. There is a possibility that it will grow out close to six months to a year in age. Even if it does, I wouldn't breed it because it'll pass this down.
On a different breed of chicken...