I thought I understood how Contagion and Unearth worked together.

So i love the interaction between Unearth and Contagion, its very satisfying to watch all those little bone constructs spreading my plague all over.

However, i noticed when i added the support gem Chaotic Freeze, that it would only show the freeze buildup indicator when i casted Contagion, not when it was spread by my little guys.

Is this a bug? Is this how its supposed to work and I just don't understand?

If that is how it works, then is it spreading level 1 Contagion when i have mine leveled up to 17? does my Hourglass gem also just not work then?