After all these months I finally noticed an issue with banding on the mission and news vendor images. This was caused by the fact that the uncompressed tga images were saved as 24-bit. I was aware of Freelancer rendering 24-big tga images poorly because I previously did experiments with tga starspheres and nav map images. However, I never noticed anything amiss with the news and vendor images, so I didn't bother changing them. But now I finally noticed it. So I've converted every images to dds DXT1.