Of course, if I turn off the alpha in the viewer it "seems" to work but at this point if I want to see "only" the alpha channel I can't. In theory, if I want to see only RGB using a node that does not "multiply" as Set Alpha or SeparateRGB + Combine RGB I would expect to see the "RGB" (and not "RGBA") data intact without the influence of the alpha ( alpha which seems to be added more than multiplied). The alpha channel, however, should be kept waiting for a node like "Convert Alpha" which multiplies by RGB.