Displacement for cube It sounded so simple to use displacement for a cube, but I found there were a lot of question about that.
I would like to model a cube with imperfect edges. So I made a base model like this:



It had beveled edges:



I sculpted a hires cube and created imperfections along the edges and the faces: 



I generated a displacement based on the simple cube. Of course it had to have UVs. I used the default UV layout:



The beveled corners looks like this in the UV editor:



I generated displacement map with the default Blender Render engine (v2.79). And it seemed OK. 

But the rendered image had some problem with the edges:


I tried to subdivide the base geometry but it did not solve the issue.

How can I fix that problem?

What would be the ideal workflow for this (stressed cube) task?
I would suggest baking the high poly mesh to a normal map in Cycles and plugging the generated image into the material for the low poly box using the node editor. There are many great tutorials on this workflow, including: https://youtu.be/BOYRCI-dtjU. It produces consistent results.

You may want to triangulate the low poly mesh first if you are going to export it to a game engine such as Unity, as they may calculate triangles differently.