PHost condenses messages. You get only one report per object, not one for every ship which scans it. Therefore it can't compute sensible distances. After all, you can compute these yourself on your starmap.
Some programs which parse messages expect them to come in a certain, fixed format. For these programs, PHost fills in the dummy value "999 ly".
If this annoys you, change your language to "NewEnglish" using the language command.
