Blender to Unity animation exporter problems..

Hello

I have a skeleton and some animations that I export from Blender, and it works.
Problem is, that if an animation only affects ex. left arm the Animator window in unity shows that
that animation consist of all bones in the avatar, when it should only contain one or two. Is it an error in Unity or perhaps Blender ? Or am I missing something here ?

 

perhaps avatar masks are what you are looking for?
https://unity3d.com/learn/tutorials/topics/animation/avatar-masks