Other mistake: When Undercover Brother is being tested for his knowledge of the white man's culture, he's asked (something along the lines of) "on 'Friends' in season 3, Ross sees something of Julia's that makes him feel bad for kissing Rachel the night before." It was Julie, and the second season.
Plot hole: Shortly before the penultimate fight between Feathers and UB, Smart Brother comments that UB has a few seconds before the reactor goes. Yet, no matter how loosely SB's words are interpreted, the whole sequence from when he said that to when it blew lasted longer than "a few seconds".
Revealing mistake: Just after the B.R.O.T.H.E.R.H.O.O.D. discover who UB is, it cuts to UB in his apartment, apparently having a kung-fu moment. As he jumps backwards into the wall, it wobbles quite badly (as do the parts mounted to it) - obviously just a piece of free-standing plasterboard.
Audio problem: When UB is running through the things that have been done by "The Man", in the Chief's office (ie. NBA 3-point shot, Spike Lee), after UB says "So the entertainment industry really is out to get Spike Lee", he says "Is that right?" but if you watch UB's mouth, he is not saying this line.
Continuity mistake: In the scene where UCB first arrives at "The Brotherhood" the medallion he is wearing changes three times: a lion fang, a small gold disc, and finally when Chubby Brother is showing UCB the modifications to his car the large disc with the fist raised that his father gave him.