@jk_blaqcat CUBE has officially said B2ST was not correct (cf. CubeUnited facebook, 120829):
Fun Fact #1: Do you know the difference between BEAST and B2ST. Many believe that B2ST is the name of the group, however, that is incorrect. The official name of the group is BEAST (all caps) and the official logo of BEAST is B2ST! Have a wonderful Wednesday!
Well they also officially changed it to "BEAST" before debuting, and there's already a bunch of BEASTs out there. Until they figure out a way to separate artists with the same name, last.fm will always be cluttered. Neither tag is wrong; just let people tag how they like.