It seems we have an issue with the Counter Top as a type option in Cabinets.
If you add a new cabinet and select Type = Counter top (or try to change one already in the model), you can change the details (size, backsplash etc) in the Catalogue and it will keep the settings, but as soon as you insert it into a model it will revert to the default settings (1800mm x 500mm with a backsplash etc).
When the counter top is part of the cabinet itself, it works OK.
Until this is fixed it you can create one using a piece of floor (drawn 'by picking points'), set thickness and elevate. In some ways this is more flexible than the counter top anyway, as it can be any shape. (EDIT: - see how to do it in this post
http://forums.turbofloorplan.com/index.php/topic,1297.0.html).
Allan