Reproduction steps:
1. Open the attached project;
2. Select "SelectMe" in the project;
3. Click "1.Create and set sprites" Button in the inspector;
4. Fine images and valid references are set;
5. Click "3.Modify sprites" Button in the inspector;
6. Broken image and missing reference are set.

Expected results: the sprites should be modified normally;
Actual results: the references of images are missing and images are broken.

Reproduced on: 5.3.6p6, 5.4.4p3, 5.5.1f1, 5.6.0b9