Character mistake: At the end of the episode when all the kids line up to head upstairs, Mike gives instructions to line up according to their size (big to small). If you notice carefully when the kids all line up, Peter stands behind Marcia, yet he is slightly taller than her.
Character mistake: When the Brady kids are practicing for the talent show, instead of saying, "Come on, Pete," Marcia says, "Come on Chris," which is the actor playing Peter's real name (Christopher Knight). (00:14:30)
Character mistake: In the courtroom, Cindy and Bobby are repeating their fight over spilling ice cream and Cindy says "You spilled ice cream on my dress" but at the start of the episode when coming home from the store, Cindy is wearing pants, not a dress.
The Voice of Christmas - S1-E12
Character mistake: Alice is in Mike/Carol's bedroom trying to find a place to hide a present and can't find room in any closets and chooses under the bed (only to find Bobby there first with the same idea). Why couldn't Alice simply hide the present in her own room?
Character mistake: While they're dancing and practising in the garage Marsha says "come on Chris", when she should have said Peter.
Answer: There were several episodes throughout the run of the show where Marcia was infatuated with a guy she went to school with. This bracelet could have been a gift from her then-boyfriend; as such, she would not want to take it off, as a sign of loyalty. A stupid thing to do, of course, but it's not a mistake for a character simply to be dumb.
Matty Blast