Cant use soften brush in texture paint mode

Hi, I have been texture painting this same way for several weeks with great results. However today I am having some kind of glitch. There is a tiled skin texture with 3 other textures set up to alpha over the tiled texture. The other 3 textures are for details like freckles and stuff. when I try to soften the layer that has color and alpha, the whole texture goes black in that area I have attached a screen shot that shows the setup. Any ideas?

Changing the aplha setting in the UV window from pre multiplied to straight seems to make the problem go away. It did not matter which mode I used. I think switching it just made blender re load the alpha channel.