I've been using Photoshop for a little over a year and suddenly yesterday my layer mask did something it's never done before. I'll go over the image with black, but when I go back over in white, it comes back faded. My brush is at 100 opacity, 100 flow. The image and layer mask are both at 100 opacity. Why is it suddenly doing this and how do I make it stop?
I can tell from your second screen shot that it is not pure white. You can actually see light gray surrounding the white of the first image. Hit the D key for default 100% black and white and try again.