Double chest splits when pushed by piston/slime.

I was playing on my Minecraft world when I built a flying machine. I attached a double chest to the slime, and as it was in transit, the chests were split. I stopped the flying machine and the chests still remained bugged   

Why did I do this, you ask? Well, I DON'T KNOW. 

Username: "ToastySix399425"

Footage (Building for proof)

Footage (Bug)