Continuity mistake: At the beginning of the movie when Flash and the Ebony Sparks are performing, you can see behind Flash, the back-up singer on his right (our left) throw his red sports coat and bow tie on the ground and rips open his shirt. Then when they show a close up of the back-up singers he has it buttoned but is in the process of taking it off. Then when they focus back on Flash, the man's shirt is clearly open, then they go back and he's still trying to open it up and he finally rips it off and goes in the motion of throwing it, but then (less than second) it pans out to show the whole group jump up and do the splits at the end of the song and the man has the shirt on again.
Continuity mistake: While in a hotel, Jimmy the manager is talking to Flash as he stands in the doorway of his hotel room. Eddie comes down the hall and Flash leans against the door with his shoulder. In the next shot, he is leaning against the door with his hand, in the following shot, he is back to leaning with this shoulder.
Revealing mistake: There are brown pieces of paper that the brother has supposedly been writing songs on (when his sister is in the room cleaning). She picks up the papers and starts to sing, and he flips one of the pieces over as if they have writing on both sides. Only there is no writing on them, even though she is singing the lyrics he has written.
Continuity mistake: When Eddie kisses the girl (who was supposed to be booing him) at the Apollo, she faints. After a while, they cut to the group's POV and she is sitting up in her chair fully awake. Then they show her again and she is now down again, then up and finally at the end of the song she is down.