Creepers are not exploding in creative mode

When I pick up any Creative maps I have created or downloaded, when a Creeper get hurt by me, he's not acting like it have to act (not approaching and explode if the player stand still or is in the area where the Creeper can act)
Even if I try to change the difficulty (easy, normal, hard)
I don't know if this is normal or if it's a bug, because the other mobs are acting normally and are becoming hostile..