That's weird, you're right the EPA says to just use soap, but like every other site I found said to use bleach,
for example:
http://www.ehow.com/how_113168_remove-mildew-walls.html
This is just a bedroom wall, there's no water sources, but it is an old building with cracks in the wall and everything so who knows. (the other side of the wall is the outside of the building). The garage is under the bedroom and it flooded a while ago so that could be related.