How to reproduce:
1. Open any project
2. Set Main Camera > Clear Flags to "Don't clear"
3. Create a 3D object
4. Add Vulkan to Graphics APIs for Windows and move it to the top of the list
5. Build & Run Standalone, play

Expected: Everything is rendered correctly as it would be with Direct3D11
Actual: The background is glitched out and flickering (as shown in "onecam.mp4")

Reproduced with: 2017.2.0a1, 2017.2.0f3, 2017.3.0b4, 2018.1.0a1
Not reproducible with: 2017.1.2p1, 5.6.4p1
Regression introduced in 2017.2.0a1

Note: Setting Clear Flags to "Depth only" gives the same result
Note: I added a video "twocams.mp4" showcasing the objects glitching out in a different way. To reproduce it:
1. Duplicate the 3D object and add a new layer to it
2. Create another camera
3. For the Main Camera, set Clear Flags to "Skybox" and Culling Mask to "Default"
4. For the second camera, set Clear Flags to "Don't clear" and Culling Mask to the new layer
5. Build & Run Standalone, play

Won't Fix because the solution results in performance drop on Mobile devices.
"The only way we could prevent this from happening is to force the store action to store both MSAA and the resolved version every time, and this would totally kill performance on all mobile targets, so it's not an option."