Repro steps:

2. Open and close the project to create a Library folder and all .meta files
1. Open the "UnityPlayerIcon.png.meta" file with a text editor
2. Scroll down to "User Data" and delete "this is a sprite"
3. Delete the Library folder
4. Open the project
5. Open the "UnityPlayerIcon.png.meta" file
6. Scroll down to "User Data"

Fixed in: 2018.2.0a1

Expected result: "User Data: This is a sprite"
Actual result: "User Data: "

Reproduced with: 2017.2.0f3, 2017.2.0b2, 5.6.2p2, 5.5.4p1, 5.4.5p4