Scaling with alpha channel

Hi there, I’m using SGE for scaling/rotating surfaces, but I’ve a
problem. It doesn’t use the alpha channel of my surfaces!

I’ve a surface with an alpha channel (orig_sfc), and I want to draw it
four times bigger over another one (dest_sfc), so I call:

sge_transform(orig_sfc, dest_sfc, 0, 4.0F, 4.0F, 0, 0, x, y, 0);

and I get a horrible black border (that is suposed to be transparent)
around my image. I’m sure that the alpha channel is right because
drawing the surface like this the black border is not drawn:

SDL_BlitSurface(orig_sfc, 0, dest_sfc, &d);

is this simply that SGE doesn’t support alpha channels? or is my problem?