I have just updated minecraft to version 1.9.

In my base I have 3 chicken jockeys captured. I found that the zombies were no longer riding the chicken, but frozen mid air in a standing position, the chicken could move around fine. This is probably the result of me using an external world editing program called MCEdit.

I killed the zombies and tried using commands to spawn in new chicken jockeys. But the command only produced a regular baby zombie. I tried using the command both in chat and with a commandblock, same result. I also tried spawning zombie pigmen jockeys, and here the command only produced a regular baby pigman too.

I tried the command in several of my worlds with the same result. I also tried the command in minecraft 1.8.9, where it produced proper chicken jockeys like it should.

I also found that spawning a chicken jockey in minecraft 1.8.9, and then opening the same world in minecraft 1.9, preserved the chicken jockey in a working state.

I have attached a picture of the 2 scenarios with the commands visible in chat(to make commands visible i removed the slash in front of the command)