Playback error on pigs in certain circumstances (resolved)

I created a machine in the hope of making a "Canyon of mobs", so I decided to test the pigs first.I placed several pigs onto the machine and activate the piston. When I tested, began flying several pigs (of course), the weirdest is that baby pigs started to leave together!

Note: I haven't used wheat or carrots in the pigs.

Note 2: I also discovered that if you use a pig egg on top of a pig, creates babies swine! And if you use an egg of a certain type of mob himself, also creates babies! Example: using a sheep's egg in a sheep, creates babies sheep.

Thanks Tails! If possible. some moderator, deletes my post or close the session.

"The translation of my text might not be 100% correct"