I think I have 'stumbled' upon the problem, but still don't know why? I have had cause to re-install Microsoft Office and, since then, the initial problem I posted no longer seems to exist. I have no idea why this happened, or indeed, corrected itself, and can only assume it's something to do with the recent updates, which is when this issue began.
Just for your information. When I do a 'factory restore' I always uninstall Microsoft Office that's pre-installed with the machine and then install my preferred version - Office 2007. In my case the pre-installed version is Office 2010 and I use the Office Uninstaller / Clean Tool to uninstall so there shouldn't be any remnants left over. I have done this for many, many years and...