haven't been able to get a determined criteria for which type of mob will suffocate and which type will not. screenshots below with hitboxes on and off.
MC-84339
Some types of mob under levitation suffocate in ceilings while others don't
Resolved
Duplicate
1
(Unassigned)
Confirmed
Minecraft 15w31c, Minecraft 15w41b, Minecraft 15w43a, Minecraft 15w44a, Minecraft 15w44b, Minecraft 15w45a, Minecraft 15w46a, Minecraft 15w47a, Minecraft 15w47b, Minecraft 15w47c
Retrieved
Still present but the Cow is fixed