hello, i was just going to write about this uvrandomiser and displacement problem as well so I can tell you:
i m using corona 4 hotfix1,
as you can see on this pic i attached,
corona multimap is working perfectly with "mesh element" mode,
but the "uv randomiser" in "mesh element" mode does not work on the displacement map
it is working on the full object, but not on different mesh elements of the object.