I should add.....
Everything seemed fine immediately after the update. It was a few hours after that the problem started.
The widgets alternate with the control pannel roughly every second. I have checked the settings on my online dashboard and nothing has changed there.
Also, I wrote earlier that the control panel will stay on screen and that is wrong. It is only the sub-menus that remain onscreen. When I go back to the control panel the alternating thing starts again!

Thanks for that Duane.
Mechanically, the top button seems to be working exactly as it always has. It moves freely and I can hear a faint clicking as I press it. The screens go on alternating though despite my wriggling the switch in all possible ways!
Could it be a loose connection internally?
Is that easy to get at or should I return my new little friend?

Solved, in a wonderfully tactile chumbyesque sort of way!
In increasing frustration, I gave the thing an extremely firm squeeze, it hiccupped (it gave a loud click) the screen flickered, and then it all settled down to normal again.
He he!