Metadata Navigation not working elsewhere than site settings

I'm coming to a really strange behavior of SharePoint 2013 Metadata Navigation. I have set a list of terms for the top navigation, at the "root" of my site (aka the highest level of SharePoint, http://mysitecollection)

So, i wanted this top navigation to display my levels like:

- level1 A
- level1 B
   |- Level2 B.1
   |- Level2 B.2
- level1 C
   |- Level2 C.1
      |- Level3 C.1.1

And getting those little submenus.

But this does only work when I'm on a site or library/list settings! I don't see it display on home, for example. On home, I only see level 1. But absolutely no level 1's children...

Do you have any idea on what is happening?

Do you have any idea on how to fix it?