SDL_BlitSurface, ALPHA, behaviour seems inverted


i created an SDL_Surface with alpha channel. I use
SDL_BlitSurface() to blit a “sprite” (a small SDL_Surface)
with alpha channel into this surface.

At positions in the destination Surface where the
image is opaque, the “sprite” is drawn.
At positions in the destination surface, where the
image is transparent, the sprite is NOT drawn.

It seems an alpha value of “transparent” in the target
surface prevents the sprite from being drawn.

This looks inverted to me, i read about SDL_SetAlpha,
but this doesn’t seem to influence the behaviour.

Best regards,