Alpha channel being ignored in custom operator

[jcallina]

I am seeing this issue on both Windows 7 and Ubuntu:

Here is my custom operator.

class Fleximage::Operator::Snap < Fleximage::Operator::Base
   def operate(caption = nil)
   photo_frame = Magick::Image.read("public/images/frames/snap_master2.png")[0]
    @image = @image.resize_to_fill(150, 180)

    @image = photo_frame.composite(@image, 17, 17, Magick::OverCompositeOp)
  end
end

When this is executed any alpha in "public/images/frames/snap_master2.png" is rendered in black. I have tried to recreate the image in several ways with similar results.