To reproduce:
1. Open attach project;
2. Select "SelectMe" in project
3. Click "1.Create the sprite of star image" Button in inspector
4. Check preview of SelectMe and Sprite assets. There is fine image
5. Click "3.Modify the sprite to circle image
6. Check preview of SelectMe and Sprite assets. There is broken image

Actual results: The image is broken or does not appear at all.
Expected results: When "3.Modify the sprite to circle image" is clicked the circle image appears.

Reproduced in : 5.5.1f1; 2017.1.0a2; 5.6.0b10; 5.4.4p2