Steps to reproduce:
1. Download and open the attached project
2. Create a new script
3. Add the "xy" icon as the script icon via the Debug menu
4. Save the project
5. Restart the Editor

Expected result: script icon stays
Actual result: script icon gets set to the default one

Reproduced on 2017.1.0p2, 2017.2.0b5, 2017.3.0a2

Notes:
-Recompiling the script also makes the icon get reset to the default one