Package list disappears on changing package view filter from 'All Packages' to 'In project' or vice-a-versa when packman window is not docked

Steps To Reproduce:

1. Create a new project
2. Windows > Package Manager(Leave the window undocked)
3. Package Manager > Change "All packages" to "In Project"
4. Click randomly on any package from the available list

Note: If packages don't disappear, change filter to All packages again and click on random packages

Expected Result: Clicked Package is selected

Observed Result: Clicked Package is selected but some of the packages disappear

Reproducible On: 2020.1.0a3, 2019.3.0b2

Not Reproducible On: 2019.3.0b1

Environment: Occurs Only on Mac