Creeper Explosion

In the previous versions of Minecraft, when you are fighting a creeper and it is starting to explode because the player is near it, you could walk back a couple blocks and the creeper would stop the process of exploding itself. Now in this update 1.2.7 when the player walks back a couple blocks away from the creeper, the creeper still explodes, I'm not sure if this is a bug or if the creeper mechanics has changed prior to this version of Minecraft. It is annoying when you are trying to kill a creeper with a sword.