Operating system: Darwin-19.3.0-x86_64-i386-64bit 64 Bits
Graphics card: AMD Radeon Pro 560X OpenGL Engine ATI Technologies Inc. 4.1 ATI-3.5.5
Broken: version: 2.83 (sub 11), branch: master, commit date: 2020-04-03 00:24, hash: rB6f4dbb661f10
Worked: (newest version of Blender that worked as expected)
Short description of error
If you're panting on Weight Paint, change the Brush size, then paint and undo the undo also affects the previous size change.
Exact steps for others to reproduce the error
Open the default file, change to weight paint, increase the brush size, paint the cube then undo. The brush size will get back to the previous size along with the undo on the paint.