unexpected result when using Image.composite

I am using Image.composite to combine two images and am getting
unexpected results. Partially transparent areas are appearing
discolored. When I preform the same operation in the Gimp, the result
is as expected. A script demonstrating the problem is

import Image

fg = Image.open("a0001.png")
bg = Image.open("bg.png").resize(fg.size, Image.ANTIALIAS)
Image.composite(fg, bg, fg).save("out.png")


I have attached the source files for reference. Any insight into this
problem would be appreciated.
Edward Cannon

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