Reset should change the settings to what the LR defaults are. If you applied a preset during Import then the initial rendering would be different than the default rendering.
In Before/After mode, if you flip the before and after using the double-arrows at the bottom left, do the toning sliders change?
Thanks. Not sure. I deleted the image from the Lightroom catalog, deleted the image file sidecar and re-imported and that solved the problem. But now I don't really trust Lightroom.
I've decided I'm much happier using Bridge and Photoshop CC.
Thanks for taking the time to help.
While it would be awesome to find a bug and have Adobe fix something, I suspect it is the mystery borne of inexperience.
Deleting the history steps was the one thing that removed the evidence trail that would have helped determine what had happened.