I am using Blender 188.8.131.52. During character creation process, after rigging, whenever I add shape keys and then modify the mesh with Proportional editing, in edit mode. It is found that proportional editing always give influences in a mesh which is far away from the desired area. I don't know whether this is glitch in Blender?
I was facing the same problem. It is not a glitch, the problem is that Blender uses the rest pose to compute neighbor vertex influence, this is why editing vertex on a posed mesh can be so awkward (proportional editing, smoothing, etc.) The solution I found is the following one:
- Pose the character the way you need.
- Create a new shape key.
- Click the "V button" in the shape keys panel and select "Create duplicate for editing". This will create a new linked mesh, without armature and without shape keys, but with the shape of the posed mesh.
- Edit the new mesh to achieve the shape you need. Now you don't have the editing issues mentioned before. You don't need to create any shape keys in this new mesh.
- Once finished, go to Object Mode. Select the "clean mesh" and then shift-select the original mesh.
- Go to the shape keys panel and select the shape key you are working on. Click the "V button" and select "Add as corrective pose-shape (slow, all modifiers)".
- Finished! You have a shape key that works correctly on the posed mesh.