Skinned mesh doesn't follow its extra bone ?

Hello,

I have an archer with a bow bound to bow_bone. The bow uses a Skinned mesh renderer.
With legacy system, if I move bow_bone in the editor, then the bow follows it.
With Mecamin (with both Generic & Humanoid modes), it's impossible to move the bow, even if bow_bone still moves correctly. Actually, the bounding box of the bow moves, but its vertex don't, so on screen it looks like it doesn't move.
Disabling Animator doesn't change anything.
Removing Animator lets me move correctly the bow through bow_bone.

Moving the bow directly doesn't do anything with both Legacy & Mecanim, which is understandable (ie: the vertex positions actually depends of the bone position). But I don't understand why the bow doesn't follow bow_bone when Mecanim is on.

Anyone could shred some light on this ? Or even better, have some way to make it work like expected ?