Bug in Unity3D humanoid auto-configuration

1: Download this cowboy character, and ensure it is rigged as a humanoid
https://www.assetstore.unity3d.com/en/#!/content/90595

2: Find a piano playing animation on Mixamo
https://www.mixamo.com/#/?page=1&query=piano

3: Download the animation twice. Once with a skin, and once without a skin.

4: Import both animations into Unity, ensure both are rigged as Humanoid

5: Create an Animator for the cowboy, and instruct it to play both imported animations in sequence.

Expected: Animations should be identical.

Actual: The animation imported without a skin animates the character with mangled fingers and a strange body pose.