I know the reason. POtted version. B5 was filmed on film in wide screen format. The idea was that it could be transferred to a HD format.
Special effects done to NTSC 4:3 format, the idea being that when the HD/Wide Screen version was needed, they could be re-rendered. The files for the effects were lost in the mean time

. So any scene on the DVD which has CGI elements (this seems to include captions and credits) are taken from the NTSC 4:3 composites, which are upscaled so that they will fit in the 16:9 format. The result on PAL is awful as NTSC has fewer horizontal lines.
Result: poor image quality on a lot of scenes, even between cuts in the same scene.