This does seen to be a bug. Can you upload the two layers .png so i can try to see what is going on?
Just in case, i will leave here how it work.
- Take this pic, open in photoshop, paint.net or any other image editor.
- Cut the hair, add to a new layer. Must have a transparent background.
- Save each layer as a .png image. The hair layer must have a transparent background. Both .png files must have the same width and height.
- In the background layer. Add the full image without the hair.
- In the second layer, add the hair.
In the next version, it will be a few improvements for the layers. Like adding transparency and changing the Z index of each layer.