System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 980/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 441.20

Blender Version
Broken: version: 2.82 (sub 6), branch: master, commit date: 2020-01-08 16:23, hash: rBe72ecaa37157

Short description of error
Tried making a custom brush that would function as a clay brush with the Fill brush as an experiment. When I then tried to undo brush strokes with undo the brush all of a sudden lost its custom name and settings.

Exact steps for others to reproduce the error

1. Create a custom brush.
2. Start using the brush on your sculpt a couple of times.
3. Press undo as many times as you used the brush.
4. The custom settings should be reset back to default.