I've noticed it many times. When you apply a gradient map in Photoshop to any image or layer, the opacity doesn't work for any points (highlighted in yellow).
Basically, I want one color to be 100% opaque, and other should be 100% transparent, so it doesn't affect unwanted areas of my image.
But when I tried to move the opacity slider or bring down the value to 0%, it didn't show any change. Why is it so?