This is a continuation of a post that was closed prematurely: http://www.kriesi.at/support/topic/override-sidebar-position-for-shop-pages#post-71817
It appears that the issue with all the solutions suggested to date is that the is_shop() function is returning false when invoked from the product category pages. As such, the sidebar is being generated with class=sidebar_right instead of class=sidebar_left.
It is unclear to me why the is_shop() function is returning false. Perhaps there is some other way to detect the presence of the product category page so that the suggested solutions will work and the sidebar class will be correctly set to sidebar_left?