I tested all mob that are spawnable with the spawneggs but all mobs were kill able. I think it doesnt work only if the mobs spawn normal (without using the spawneggs). the mobs that didnt die in the pic was an Bat and a Creeper.
PS: i tested the mobs spawned by the spawneggs in an other world ...maybe the other world was broken
I created the world in 14w33c and didnt open it in an other version and i also didnt transported the mobs dimensionally... i didnt build a portal or something else