Steps to repro:

1. Open Unity on Windows 10 with -force-glcore mode;
2. Right click in Project tab Import Package -> Network (though you can choose any of those);
3. Click Import button;
4. Observe Game view window.

Actual result:
After package import Game view window goes black (see attached gif video and actual.png).

Regression introduced in Unity 5.4.

Expected result:
Game view window should not become black after importing package.

Workaround is to restart Editor and reopen project.

Notes:
- Reproducible in: 5.4.0b6, 5.4.0b5, 5.4.0b4;
- Reproducible on Windows 10;
- Also reproduces when importing any package by double clicking on it or dragging it to the project folder;
- Not reproducible in DX11 mode;
- Not reproducible on OSX (GlCore);
- Also reproduces when switching graphics API (from DX11 to OpenGlCore) in PlayerSettings.