Unity closes on clicking close button in Popup appears after minimising Package manager window

Steps to Reproduce:

1. Create a new Project
2. Open Window > Package Manager
3. Dock Package Manager window
4. Select Package Manager window and click Shift+Space to maximise
5. Select Package Manager window and click Shift+Space to minimise
6. Click on cross button

Expected Result:
Popup closes

Actual Result:
Unity Editor closes

Reproducible on: 2020.1.0a15

Working fine on: 2020.1.0a14, 2019.3.0f1

Environment: Windows 10 and Mac 10.14