buffer soft shadows bug

Hi, yesterday i have rendered a old scene with 800x600 resolution, later i changed the resolution to 1600x1000 and i noticed all the soft shadows from the spot lights became sharp, why? Is this a bug only in blender or is it normal, does it happen i other 3d software too?

Are you sure you’re viewing the image full size? I had a similar problem with aliased edges in the render window but when I opened the render in Photoshop it looked fine. Blender doesn’t seem to apply the antialiasing if the render is reduced to fit on screen.