The default sidebar is always called during the "products page" and the "checkout" pages, i.e. the shortcodes. I have tried to fiddle with the php code, but cannot find the exat area where the seemingly wrong test is made or it can be commented out. I am stuck in function "wpsc_products_page" in the theme.functions.php file in the wpsc-includes folder.
The pages have been setup with "Full Width" in the Page Layout setup. It works fine for "Transaction" and "Results" but not the other two.
See test mock-up on http://test.creativelooks.dk
(one other thing -> how do I control the width of the products view? I would like to have the "checkout" part by about 25 px shorter).