It turns out I'm not the only one having this problem. That particular update (and its' associated predecessor) have been a bit of a problem for a number of people.

I tried the Update Troubleshooter - it says it fixed most of the problems, but not the one I'm having.

There are a couple of complicated fixes but I didn't have the heart to try them.

Then I stumbled across someone's note on some web page - he sez he just did the old right-click/hide routine. So I tried it and, hey,presto! Update gone, never to return. All is well (so far, anyway)

It seems MS has been having problems with their update procedure for some time now. Oh well.