Blend modes and Setalpha

I've put these in as bugs but I could have misunderstood something.
First (a good thing) Setalpha affects lightblend although it's not documented.
Second (a bad thing) Setalpha <= 0.5 will cause a maskblend image not to appear.

Graphics 640,480,0
Local img:TImage = LoadImage("b-max.png")
SetBlend maskblend
SetAlpha 0.5
DrawImage img,0,0
flip
WaitKey()

The second bit is mentioned in the SetBlend docs :)

Ok, but that would mean that AlphaBlend is *always* in effect except for SOLIDBLEND. It also affects shadeblend, lightblend (good for day/night changes) and, as seen, maskblend.
Does this mean that Alphablend changes all the pixels in an image to the setalpha value?
It's very possible the doc is just a bit unclear.

No, the alpha value at each pixel is modified in some way (multiplied, I think) by the SetAlpha value (which defaults to 1.0).