They were checking the live singing by listening to the MR removed. They never said that Beast LIP-SYNC!! They said that in order for the song to be more pleasant & easier for the boys to dance, they just don't sing it ALL THE TIME. They used the technique "Fade-in" where the first part of the line have background vocals & they will sing it in the last part of it. The MCs even praised them & acknowledge their live singing skills. They're impressed how Beast can sing & dance at the same time perfectly during the Yoo Heeyeol Fiction video. Maybe it was wrong for them to do this to Beast instead of other groups, but they never said Beast lip-sync on music programs. I don't want Beauty got the wrong idea. I just want to try to help explaining what happened on the video.