Changing the Mac Game Icon in the project settings does not persist in Development packages of the project

Changing a project's Mac game icon does not persist through Mac development packages of the project. However, Shipping packages will show the correct icon.

This only occurs on Mac. This was not reproducible on Windows.

Regression: Yes

Broken: 3084973
Works: 4.12.5 3039270 (Can regress further upon request)

1. Create/Open any Blueprint template project
2. Go to Edit > Project Settings
3. Under Platform > Mac change the Game Icon to the attached .icns file
4. Close the Project Settings window
5. Under File > Package Project set Build Configuration to "Development"
6. Now package the project for Mac
7. Locate the packaged .app

Result: The .app's icon is the default Unreal icon instead of the icon set in the project settings