Chickens suffocate in trapdoors in vertical position

Rabbits also seek out Trapdoors in the vertical position, but are unharmed.

EDIT: Also, 20 rabbits are all trying to go through the trapdoor at the same time instead of roaming around their cage.

Thanks for the report; however, this is a duplicate of MC-50556 (the fact that mobs will try to do the pathfinding under trapdoors) and MC-150401 (that chickens die under a block).