Newbs don't know about this feature. It's not a bug. Just an OP Dark Seer ability if used correctly. There are a ton of videos of people going around doing this. This is just one I stumbled upon now. Not the best, but it teaches you about it if you didn't already know.

Dark Seer's Vacuum does small damage and moves everyone in an AoE of where it is cast to the point at which it was cast (even if that point is cannot be walked to).