Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 1060 3GB/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 417.35
Broken: version: 2.80 (sub 74), branch: blender2.7, commit date: 2019-06-16 23:08, hash: rB12da679fa094
Short description of error
When you activate "x-mirror" under "Options" in Editmode and switch to Weight Paint Mode, the x-mirror stays active for all weight paint actions even if symmetry is turned off in the Symmetry options (of the weight paint tool) which is very missleading... (took me half an hour to find out why there is a mirror on all my weightpaint strokes)
If x-mirroring is turned off in Edit Mode, everything works as expected.
Exact steps for others to reproduce the error
Create a new blend file.
Subdivide the cube a couple of times.
Go to Edit Mode.
Check "X-Mirror" in the active tool settings.
Switch to Weight Paint Mode.
Switch to front view.
Add some weights with the brush to some of the verts in the cube.
--> brush strokes are mirrored even if Mirror in Symmetry is turned off