bug fix when learnee's mutations ballot are the same with learner's
bug fix when learnee's mutations ballot are the same with learner's

shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN