It was to my understanding that in order to create a creeper only (gunpowder) farm, it was necessary to creat a 2 block high area without light sources with trap doors on the ceiling (to keep zombies, skeletons  witches, endermen, etc. from spawning) and sporadic carpets on the floor to break up any 3x3 area (to keep spiders from spawning), with a cat or ocelot in the center to scare creepers off the edge . However that is not the case in the current version. Any hostile mob that can normally spawn in a dark 2 block high area is able to spawn under these conditions including spiders. Also if and when creepers do randomly spawn they are not scared of the cat/ocelot and do not mind it's presence. Please fix this bug so that hostile mob spawning conditions are back to how they used to be