Perfect; many thanks. When I changed 'Current' to 'Current & Below', behavior returned to what I normally had in prior installations. I also had to select the background layer on which to make the clone-stamp corrections. Without that, there was no 'action' whatever (probably for obvious reasons[!]).
In answer to your other question, no; preview was not showing anything; just white (or lack of content).
Glad it is sorted.
With sampling set to All Layers or Current and Below you should be able to clone to an empty layer. It is good practice to do that as it does not destroy pixels and can easily be undone later.