A pigmanjockey is not visible on a chicken.
This video will show you what I mean:
https://www.youtube.com/watch?v=HjUyy-z5jEc
UPDATE
when you log out, or unload the chunks and then load them back in, the baby pigman will be there! (After you kill the chickens)
Environment
Windows 10, java 8 update 60
Linked issues
Comments 2
Possible duplicate of MC-91388.
Doesn't work for artificially spawned version(summon command/spawn egg). Must have to be spawned naturally.