GP2X Sdl_displayformatalpha Function

[joyrider]

as far as i understand sdl_displayformatalpha function prepares the surface for fast alpha blitting and i should set the alpha value before calling the function. I have SDL_SRCALPHA flag set and i have a alpha value of 0 so the image would become completly transparant (just for testing purposes). Now nomatter what i do (calling sdl_setalpha before sdl_displayformatalpha or after it) my resulting image is always completly opaque. The only time it isn't opaque is when i use sdl_displayformat instead of sdl_displayformatalpha but thats utterly slow when being blitted then.

I'm using payeren's HW Libs. Does anyone else have this problem, or does someone know what i'm doing wrong ?

thanks in advance