Export PNG images with alpha channel from flash

I have this FLA with animation and when played, the animation has alpha channel. I can’t understand why when I look in the library I see the frames without the alpha channel and also when I try to export/extract the image, again the image don’t have alpha channel.

How is it that in flash this image ha开发者_C百科s alpha channel and how to get it out like that into PNG?

Here is the link to download the FLA:

Untitled%20-1.fla