Thanks for the reply @RickyBlender,
The one I linked to is said to be a patched version of that one. They both have the same creasing problem, although I’ve now found that different builds of Blender seem to dictate the RGB channel order and appearance. I can’t get the original add-on to work properly in the latest experimental build of 2.79, which probably explains the reason for the patch.
I’ve made another test scene (again with flat grey image map), and have noticed that along with the creases there are smaller artefacts that change resolution depending on subdiv level:
Tension Artefacts 2.blend (567.3 KB)