Originally Posted by
monroeski
They should only be spawning in the lowest levels of the mine, as notch has been saying for weeks that the closer you get to bedrock the more precautions you'll have to take. Specifically, he said that more light than normal would be needed to prevent the spawning, but I don't know that he's actually implemented that yet; I think they just spawn when you're that deep regardless of light at this point (again: alpha build). When the update first went live people were apparently having things spawn right in their living rooms, which I believe was fixed in one of the small after-updates.
I haven't had nearly the amount of mine-spawning problems that you're having. In three or four nights so far, I've had two enemies spawn down there and they were both on the same night. That was night two, which I think was actually the first night that the mine existed (since night one consisted of me actually digging the mine); afterwards, I threw up some more torches and haven't had any problems since (which admittedly could just be due to low sample size of only a few nights).