The WBO has vacated the middleweight title held by Sergio Martinez citing a WBO rule that states
a champion who wins a non-WBO championship in weight class that is different than the weight class in which he holds his WBO Championship must decide within ten days of the non-WBO Championship which title in which weight class he will retain. No WBO Champion may hold a non-WBO Championship in a weight class that is different from the weight class of his WBO Championship.
To date, Martinez has not renounced his WBC 154lb belt. Martinez won the WBC and WBO middleweight titles on April 17th against Kelly Pavlik. He has 10 days to appeal.