System Information
Operating system: Linux-5.5.8-arch1-1-x86_64-with-arch 64 Bits
Graphics card: GeForce RTX 2070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 440.64

Blender Version
Broken: version: 2.83 (sub 10), branch: master, commit date: 2020-03-21 00:07, hash: rBa22cd6b6a951
Worked: f01bc597a8e
Breaking commit found from git bisect: c476c36e400

Short description of error
Interacting with the UI or changing the brush size/strength darkens the mask until the viewport is moved.

Exact steps for others to reproduce the error
Open the example file.
Press 'F' to change the brush size.
Watch as mask darkens until clicking to set size.

Widen / shrink the tool menu.
Watch as mask darkens and stays darker until moving the viewport.