System Information
Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 1060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 419.17

Blender Version
Broken: version: 2.80 (sub 74), branch: master (modified), commit date: 2019-06-28 15:47, hash: rBc9238e638fd5
Worked: 17 June official build.

Short description of error
Possibly after today's https://developer.blender.org/rBd44aebd3fe6e706c0c9d7938ed6f695163f268b8 switching between the different render types (scenes) in the material preview in the material properties shows poor response.

Exact steps for others to reproduce the error
Default scene, cube selected. Select the Material tab in the Properties window and expand the Preview sub panel.
Click between the various preview scene types. Note it prevents you from quickly clicking between different ones.

Note that if you click about once per second from type to type, the material never refreshes until you stop and wait.

Prior versions were very responsive, you could click quickly between the different preview types.

I feel like if you're actively interacting with the preview pane, it ought to be OK to take precedence over (or at least compete equally with) other display tasks).