Theres so many loopholes in the WBC rulebook regarding mandatory defences and time extensions , google it and theres a PDF file with all the rules.

Some good points in this article and its getting on for 15 months and he's definitely being shown favouritism by the WBC !!
http://www.givemesport.com/369662-vitali-klitschko-should-be-stripped-of-his-title