Game Mechanics: mob ghosting

[guineapig]

This happens all over and often isn't even related to the mob having been there recently.

Good examples include:

Random minotaur in Lguk dead side zone in. First it's there, then it's gone.
Random elemental pets in Sola.
Random shaman pet in SolB.

Not exactly what you are describing (although I know exactly what you're talking about) but possibly related.