You are not inverting the texture, you are changing the lighting sun direction, something that affects the material bump, normal or displacement map lighting. If you add an object to see the direction of the shadows, you could check it yourself.
Computer Graphics Software Developer Octane plugin development and support: LightWave and Houdini
Thanks for your reply. I fully understand what you say about sun direction. Having restarted my machine the problem has gone away! But as can be seen from the original 2 pictures there is a difference - one shows dark crests, the other shows dark crevices. Reloading the IPR didn't help, but as I say, restarting has fixed it. Could this be a cache issue, - cleared after restarting? Do please scrutinize the pictures again, I think you will see what I mean.