I don't recall the paint fur attribute tool to allow you paint bald texture maps. what it does is allow you to control the fur. eg comp the hair out of youe eyes.

To do baldness or even color I use the 3d paint tool in the textures menu. What I do is mark those spots with Maya paint tool than take that texture into photoshop to fix. I always get the same problem pure morning mentioned. To fix this I convert the texture to bitmap than back to rgb.

I have attached an example. All bald spots around mouth eyes and feet are texture maps that are connected to the fur disc.