Vanished players are shown when exiting the dungeon

When players in vanish join and exit the dungeon, it shows the players in the dungeon that they've left the dungeon. This is a bit of a problem for when we want to go in vanish and spectate some people in secret...

If it helps, I am using PremiumVanish. If integrating with vanish plugins would take too long, perhaps you could make it permission based instead so that players who have this permission aren't shown anywhere.