Scaling animations in Mecanim

Up till now I've been using legacy animations (for a 3D adventure game), but after being told that I should really, really, try Mecanim and won't look back I've started to look into using Mecanim.
Per advice I've found on forums I rig my models in Blender with Rigify and then skin the mesh to the 'ORG' bones rather than Rigify's deform bones so the hierarchy works with Mecanim (while still giving me the animation control of the rigify rig).

This seems to work... mostly. But my idle animation throws this error:

"MuscleClip 'commodore@idle' conversion warning: 'rig/root/ORG-hips/ORG-spine/ORG-chest' has scale animation'. It is not supported."

The idle animation scales the chest to simulate breathing. As far as I am aware this worked perfectly in Legacy mode. Does mecanim not support scaling? Is there a way around this limitation?
I was also considering using scaling for certain other animations (there's a level of cartooniness to our art style). if I want to do this, do I have to stick to Legacy?

 

use Generic rig not Humanoid rig.

 

Okay, cool! So what am I missing out on with the generic rig option compared to the humanoid one?

 

Both use Animator to control.
Humanoid rig doesn't use bone, they use muscle clip; Generic rig uses bone.
Humanoid rig can do retarget; generic rig cannot do that.

you could check out the unity manual for details'