If you are near a friend who loots the dungeon ghost while you don't have the trace, you'll see a triumph appear and can't claim it. The triumph will remain hidden permanently, from that point on. Even if you get to the ghost trace required for finishing all 10 ghosts. I have the triumph for finding all 10 ghosts without the triumph for the dungeon ghost, this will stops Lunar Memoriam from dropping. Leaving you unable to claim Harbinger unless this is fixed, this blows bungie.

The worst part is this glitch doesn't happen often, so bungie doesn't even know about it so a fix is a long time away.