About the Shadow (spoilers)

[Peanuckle]

I've got some questions about the Shadow that is chasing you through the game. It apparently became aware of you the moment you nabbed the orb, and has hunted you down ever since. I'm pretty sure that the warding rituals were just shams to get David comfortable with torture and murder, so nothing was actually keeping the shadow from him besides distance.

My question is: how did Weyer, Agrippa and Alexander keep the Shadow(s?) from coming after them? If Weyer had a whole collection of orbs, then wouldn't a veritable army of Shadows hunt him down?

Finally, what makes the Shadow stop for doors anyways? Does it not know how to work a doorknob? We could just put it in a maze and be done with it.