User blog comment:Godisme/烈火の如/@comment-117598-20120919162117/@comment-5028409-20120919171743

Yamamoto is probably one of the special war powers.So the Bankai stealing may not work on him either. Maybe because of the amount of reaitsu they have. If you think about it, Yamamoto Kenpachi and Ichigo are the ones with the ridiculous reaitsu levels so probably its too much reaitsu for the medallions to contain