I've verified this happens to me when I attempt to feed off "inactive" mobs. What's an "inactive" mob? A mob that is basically in "placeholder" mode and hasn't yet engaged in activity. A good example would be any map that has werewolves. Ever come around a corner and see a pack of werewolves feeding on a body? Until they aggro, they're basically inactive; not only can you not feed on them , but your powers and attacks don't affect them either. I've run in quick and used leap in the middle of them, but nothing happens.

While the werewolves are a good example, I've verified this happens with other mobs that are just standing around, too. Until they aggro, I can't feed off them. As soon as they do, I can...