Point is Bryan, that it's not that the tagline has been modified. The tagline says what it has always said: I wrote it myself when the site was originally set up. But until now it has never appeared at the top of every page! I had always assumed that Chateau was a template that did not display the tagline – I understand that some don't. But I wrote the tagline anyway, since I thought it might be useful for search engines.
When the tagline suddenly appeared on the site I assumed indeed that the other administrator had changed a setting: only to discover that there is no setting to be changed!