[2D] [Sprite Editor] Unable to rename a sub-sprite in the Sprite Editor

Steps to Repro:

1. open attached project
2. select Assets/spineboyBodyparts.png and open the Sprite Editor
3. select any sub-sprite
4. click to select the Name field
5. type in a new name
6. click off the sub-sprite then select it again

The Name field has reverted to the sub-sprites original name; this prevents Users from renaming sub-sprites.

Occurs on: 2018.3.0a3, 2018.3.0a6
Does not occur on: 2018.1.3f1, 2018.2.1f1