Shade's video here shows ~136 attacks per minute twitch.
In game i usually see ~130 for a full BAB character, and ~140 for a capstone fighter...
I think this (potential) bug might be a result of the way the capstone bonus to glancing blows is coded. BAB affects glancing blow damage, so by coding the capstone to artificially raise the barb's BAB it would theoretically increase glancing blow damage. But, since attack speed is also a function of BAB (as of the last attack speed change patch), that could have caused the increased attack rate... theoretically...