Hostile mobs despawn when sent through nether portals

Hostile mobs cannot be sent through nether portals. I was having fun in my creative world. I sent a Zombie pig man and a creeper through the nether portal by pushing them. But when i went through they were no where to be found. I tried sending a horse and a villager through the portal and back. They made it out OK but the hostile mobs seem to vanish.