Steps to reproduce:
1. Open the attached project "Case_1189557"
2. Navigate to Window -> 2D and open Sprite Editor window
3. In the top left of the Sprite Editor window choose "Skinning Editor"
4. Select "Tonno" Sprite from Project -> Assets
5. Double click on the Sprite in the Sprite Editor for the bones to appear
6. Move the bones
7. Notice another Sprite behind the original one

Expected results: The Sprite follows the bones
Actual results: Another identical Sprite is created when moving the bones

Reproducible with: 2018.4.0f1(2.0.0), 2018.4.11f1(2.0.0), 2019.3.0b6(3.0.5), 2020.1.0a8(3.0.5)

Note: Sprite Editor does not have Skinning Editor implemented in 2017.4