Simple Filter Alpha Maps broken?

I might be missing something obvious here, but it seems I can't get SIMPLE filters to output alpha maps that are anything else but completely white. Naturally, I use Set Alpha to assign the alpha channel, but the alpha map only renders as expected if I turn the filter into a SURFACE filter. Interestingly though, the diffuse maps are correctly premultiplied by the alpha set with the Set Alpha component.

So I tried some simple filters with transparency from the library, and they exhibit the same problem. Coffee Stain obviously has an alpha that is premultiplied into the diffuse map, but the Alpha Map is white when rendered via Render Maps. Same thing with OilFlame. Take a SURFACE filter with transparency, like Solar, and the Alpha Map renders correctly.

Then I tried saving to alpha supporting image formats like TGA and TIF to see if that could be of any help. Coffee Stain saves with a completely white alpha, OilFlame too, and so does Solar, which should have a correct alpha! So it seems FF correctly premultiplies a filter with transparency over any image you have currently loaded, but discards the alpha?!?

Also, I tried to apply it to a layer, and the result was absolutely correct:

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Crapadilla wrote: Furthermore, as described, alphas are apparently not saved out when using File > Save Image As, regardless of filter type (I tested TGA, TIF and PNG so far).

All these formats handle alpha/transparency differently -- see my test above.

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Crapadilla wrote: The Alpha Map turns out completely white for SIMPLE filters.

Here's a screenshot from my machine:

What background are you using? I used a transparent color:

Crapa, can you show me the original image / background you apply the filter to?

Hehe We'll look into file formats anyway, especially the TIFF -- I'm not sure that it should look as it looks now.

Good point, I'll add that to my list.

Well, what remains is this strange behaviour that for simple filters that dont use an image component, the default lifesaver image seems to prevent the filter's alpha map from showing, but for surface filters this alpha seems to be ignored and the 'correct' Alpha Map is rendered.

It seems that the lifesaver alpha is completely opaque. In that case, the surface filter's Alpha Map should be completely opaque as well, if it is a simple OVER operation that determines the final alpha, as it appears to be the case with the simple filters.