When PBR Graph Shader is created and the Keywords window is opened from Shader Graph Importer, it remains open even if other actions are performed in editor.

Steps to repro:
1. Create a new project
2. Make sure that Shader Graph package is installed.
3. Project > Create > Shader > PBR Graph
4. Select created PBR Graph > Inspector > Keywords

Actual result: Keywords window from Shader Graph Importer doesn't disappear.

Expected Result: Keywords window from Shader Graph Importer disappears when other actions are performed in the editor.

Workaround: Opened Keywords window disappears unless something from the editor's menu bar is selected or Play Button is selected.

Reproducible in:
2020.1.0a22 with Package Version: 7.1.8

Working Fine in:
2020.1.0a21 with Package Version: 7.1.8

Environment:
Occurring on Windows 10 & Mac 10.15.