Ok well it seems that the texture has very concise UV regions with a lot of black space in the interior. The only way I can find to fix this issue is to unhook the ‘diffuse’ map from the parallax, however this results in a less than satisfactory result to the point where the standard Epic BumpOffset actually looks preferable.
Would I be correct in assuming that this parallax effect will create seams with any textures that have unused UV space that is not around the edges?