Are Witch Doctor's hex stacks shared between players?

Recently I started using a Witch Doctor’s Blade, and I’ve noticed, that during Talos and GK battles other players’ attacks put a hex circle under the boss. It often happens even before I can get in melee range, so I’m sure it wasn’t caused by my character.
I’ve read two detailed threads about Witch Doctor’s weapons, and I don’t remember them mentioning, that hex stacks are shared between players.
Does it mean that, unless it’s caused by one of my attacks, that pink circle is just a misleading visual? Or maybe my blade is better than I thought, if there are at least two players using WD weapons?

DoTs usually are per character, not per target. Of course, FC has screwed up in the past.

They won’t stack together, though. At least they shouldn’t. (See above comment about FC.) There should be a stack for each instance of the weapon, so you have your own personal stack.