chickens getting hurt when they jumps under a 1 high block tunnel

chickens was getting hurt when they were jumping under a 1 block high tunnel.
What I expected to happen was...:
i expected that they were going to live a longer life.

What actually happened was...:
they died after 4 jumps...

Steps to Reproduce:
1. place 2 blocks upwards (needs to be a full block) and destroy the first block, and there will be a 1 high from the ground floating block.
2. place a chicken underneath.
3. make the chicken jump somehow, like put a block beside it so it will try to climb up there.
4. BOOM! the chicken sufficate i the block.