How to reproduce:
1. Create a new Unity project
2. Select the '4 split' layout
3. Attempt to resize the Inspector window by dragging it to the left

Expected result: the Editor does not flicker and no graphical artifacts appear
Actual result: the Editor flickers and graphical artifacts appear

Reproducible with: 2019.3.0a2, 2019.3.0a5
Not reproducible with: 2017.4.28f1, 2018.4.2f1, 2019.1.6f1, 2019.2.0b5, 2019.3.0a1

Notes:
Not reproducible with Direct3D11 and OpenGL
Some graphical artifacts still appear in "Not reproducible" versions but to a much lesser extent and less frequently; in reproducible versions, the issue has become much more prominent

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I have observed this issue on 2019.3.0a7with different repro steps and it occurs very frequently and doesn't look like a minor issue

Steps to Repro

Scenario 1

1. Create a new project
2. Hit Run and hover the mouse over the editor and click on random windows

Scenario2

1. Import the attached Audio FTP project
2. Run any scene while the audio mixer window is docked.

I have attached videos for both the scenarios.