Black screen if two cameras with postprocessing

Unity:2019.1.0b6

Create a new project with default 3D template, add "PostProcessing" package(2.1.4) from package manager.

Add "PostProcessingLayer" component to main camera(depth=-1),
then add second camera(clear flags=don't clear, depth=0) to the scene.

Now the "Game" view will be completely black.
But if I remove or disable the "PostProcessingLayer" component, everything looks normally.

Is it a bug or there are something wrong with my operation?

 

Maybe this is related issue?

(Case 1119198) Some Clear flags of Cameras are not working when using Post Process Layer and Directly to Camera Target is set to true

https://issuetracker.unity3d.com/is...using-post-process-layer-and-multiple-cameras