Chicken Jockey riding inside chicken

In my survival world, I had captured a chicken jockey, renamed it, and encased it in the ground. Somehow the chicken and the zombie got separated. I had not updated to 14w17a.

I'm not sure if this is a bug or not, but I haven't heard of it elsewhere, and I couldn't find it in the system, so I decided to report it.

EDIT: Because I was curious as to how this could've happened, i went into a testing world to figure it out, and after quite some time I did. It seems like whenever the zombie is underwater, it pops off the chicken.