In the Shrine of Oryx mission, Sardok appears in front of the door he enters the Shrine from a moment before the door opens, then the door opens and he and his minions come out.
Video capture on my Xbox Live profile (linked).
Maybe he uses Blink Strike... Was Sardok once a Hunter or Warlock? Hm...
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It happens mostly because Sardok has an AI that follows a path to get him out of the door and it's basically saying the start is behind the door and finish is where you see him blink.