Use Opera 12.16 or Older versions for now.
Opera 11.64 has fewer issues with skins than Opera 12.xx, which is one of the reasons I am still using it. See the skins link in my sig for more.
Opera 18 is not ready for use yet — at least not for long-term users who are accustomed to a high degree of customisation in Opera. See the Customising forum for more details.