SDL_gfx alpha blending problem


I’m currently experiencing a problem with SDL_gfx library.
Indeed, when I blit an alpha blended surface filled with filledCircleRGBA (A
argument setted to 255) to the screen surface, no problem the circle drows
itself correctly. but when I set the A argument to 254 (or lower) nothing is
drawing anymore.
Does anyone can help me ?

Thank you.–