Reading current code of that operator, it's not making much sense…
- It computes some averaged vertex normals out of select faces' normals only (without even complying to our generic, weighted computation for that).
- It then does two different loops (over selected verts of edges of faces first, then over loops of verts), to set some custom normals to those weirdly averaged vertex normals computed at step 1.
I think what it is supposed to/trying to do here is actually the following:
- For each clnor fan (i.e. set of contiguous faces around a given vertex, delimited by sharp edges, that share the same custom normal), properly compute the averaged normal from selected faces, and set it.
This will give predictable results, when a single face is selected for each custom normal it will just set to that face's normal, same in case all edges are sharp… And the 'keep sharp edges' option is not needed anymore, I do not see the reason for that one anyway, if you do not want a sharp edge, just do not tag it as such. ;)
Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 417.35
Broken: version: 2.80 (sub 60), branch: master, commit date: 2019-05-09 17:55, hash: rB427c75e4c20b
Short description of error
[I can not use set normals from faces when selecting a specific face. When I split normals/make em sharp I expect that I can control specific face normal without it interfering with the other normals, this is at least how you do it in all other 3d packages]
Exact steps for others to reproduce the error
[Split/ make all edges sharp, select all vertexes, go to mesh/normal/rotate to make all normals crazy. Now try to set the normals from one of the faces.
[Based on the default startup or an attached .blend file (as simple as possible)]