Sprite gets removed from the list if the same sprite is dragged and dropped on top of the added sprite

Steps to Repro:
1. Open attached or create a project
2. Project window > right click
3. Create > sprite atlas
4. Objects for packing > click '+' to add sprite
5. Add any sprite
6. Drag the same sprite on top of added sprite
in the atlas

Actual Result:
1. Sprite is removed from the list

Expected Result:
1. Sprite shouldn't get removed from the list

Note:
1. If another sprite is used then it works as expected

Environment:
Windows and Mac

Occurring with:
2019.1.0a3, 2018.3.0b5, 2018.1.9f2, 2017.1.5f1