It might look correct if you invert the alpha, but there is background color of a very low opacity data left in the area that appears transparent. Run your eyedropper tool over the flaky areas in the mask after you use the mask to remove the background and see how there are rgb values there where there are none in the areas that are truly transparent. That keeps one from cleanly cropping to the outline of the figure rendered. There is no easy way to bring the alpha selection up around the the edges of the object. I have been rendering twice if I had to use the firefly rendered, the 2nd time with Poser 4 renderer. It might save the alpha inverted sometimes, but it is clean and the alpha in tifs or psd files can be re-inverted in my software.