ArgumentException: GUILayout: Mismatched LayoutGroup.mouseMove error is thrown on closing Package Manager window after clicking on "View in Package Manager" tab in the Inspector.

Steps to repro:
1. Create a new Project.
2. Windows > Package Manager > Dock the Window.
3. Click on "View in Package Manager" tab in the Inspector.
4. Close the Package Manager window.

Actual Result:
ArgumentException error is thrown in the console.

Expected Result:
No errors in the console.

Reproducible in:
2020.1.0a24(0efcce64deba).

Working fine in:
2020.1.0a23, 2019.3.2f1

Note: Find attached stack trace.

Environment:
Only on Windows 10.