**BUG**
Concise problem statement: In the part editor, when multiple traces are selected, if down is pressed, they disappear. Undo does not bring them back.
Steps to reproduce bug:
1. Select multiple outlines in parts view.
2. Press down.
3. Cry.
Results: Lines disappear and cannot be retrieved with undo.
Expected results: Lines disappear.
Url:<you url here>(click the Share my works button to get it)
Browser:
Brand new interactions and interfaces. 
Easy to use and quick to get started. 
