I see this issue recently when I show the location of the dead ghost in Endless Steps for my fireteam friends. The dead ghost always show for me, who have catch this before. If I catch it, it's counts for dead ghost grimoire card (maybe for the achivement) and don't unlock a new ghost fragment grimoire card or show the card this ghost unlock. This issue occurred in the mission "The Eye of Gate Lord", but I not test this in Venus Patrol mission. Sorry for my english, but it's not my born language. Edit: Every time I play the story mission, the dead ghost is available to catch it again.