Well spotted, nudecad.
That makes sense. It would also explain why 1. the makers did not respond to my original support request and 2. why they have not responded to us here.
I can accept that some system files are regenerated between runs of Ccleaner so, I suppose, it means that now I understand what is going on, my faith in the Ccleaner's cleaning ability has been restored. On the other hand, if there is an intention to mislead the user in this way, then perhaps I should be looking for an alternative, more honest, application to use.
Ccleaner receives almost universal, uncritical, praise from reviewers and it's rather surprising that none of them have noticed this piece of obfuscation.