Reading further on the subject I believe this is a 'Pinned Site' feature in IE9 where if a favicon is moved from the favourites bar to the taskbar it opens a dedicted site such as the PCA dedicated site. Presumably my problem relates to closing down any IE9 dedicated pinned site and not specifically related just to the PCA site although havn't tried this because PCA is only site I have pinned. It only happens when multiple tabs require shutdown. Any ideas please?
Windows 10 Home vs Windows 10 Pro comparison: Here are the extra features you get in the Pro version