'Moving' NPCs

[Draenin]

Okay, so this has been going on for a while, but I've ignored it up until this point because it's really beginning to bother me.

For some reason, NPCs I've placed on my terrain maps sometimes seem to get pulled away from where I've set them originally.

That is, things like lights and torches will sometimes be offset when they're drawn on-screen. It's very irritating because sometimes wall NPCs randomly disappear, and the same goes for trees and other stuff. Sometimes flames will be hovering several feet away in-game from the torches they belong on, and I'm just wondering what is causing everything to be slightly off-set.

I have the classes for these NPCs mostly set as serverside so that they aren't just being drawn clientside, but the problem still seems to persist. Any ideas as to what might be the cause?