I have excavated a large field and surrounded it with a 3 block high wall with fire on top. I then set up a grid of torches inside the walls, with each torch separated by 10 blocks. Mobs are unable to jump my wall, except for the occasional spider, which burns up. Mobs still spawn in my field however, even though no block has a light value below 7. Is there a bug that causes mobs to spawn where they shouldn't be able to?
I don't think they are spawning next to the walls, my walls have flaming netherrack on top of them so that should provide enough light I think? I then placed torches no more than 10 blocks from the walls.
I placed more torches 10 blocks outside of my walls, and they still spawn all over the place in my completely flat field. I'm thinking this has to be a bug, so I'm going to take a break from Minecraft until the next update.
I'm now thinking that the torches/flame in the 360 version are not as powerful as in the PC version, or the mobs can spawn at a higher light level than in the PC version. I haven't been able to find any information on this however.
If it dies it will be your fault... SO CLICK IT!