Doing a:
gDriver->draw2DImage(mSource->pSurf, core::position2d<s32>(nX+mOriginX, nY+mOriginY), mRect, 0,video::SColor(255,255,255,255), true);
where mSource->pSurf is a 24 PNG with alpha channel. Using the Software2 renderer the texture is rendered properly. Using the Software1, the alpha channel is not used.