Other mistake: When Lucy is in the cafe watching the mother and her children, the mother repeats the same dialogue.
Plot hole: Tahnee was sent to boarding school when she got fired as a way to get her out of the show, but she was 17 and so isn't that a bit of a silly way to write her out? In Melbourne Australia, you can leave school if you wish at 15, so she in theory shouldn't be able to be forced into going to Boarding School.
Witness for the Execution - S2-E15
Continuity mistake: When David and Maddie are debating whether or not to help Lawrence Everett, the towel David uses to wipe shaving cream off his face jumps around during the scene. It's around his neck, then in his hands, then on his shoulder, and back in his hands, etc. (00:15:40)
Continuity mistake: Multiple times throughout the show, Kimber can be seen in quick shots with light pink hair (the same color as Jem's), when her hair color is actually a dark pink/red color. (02:00:00)
The Town Where No One Got Off - S1-E4
Visible crew/equipment: The overhead boom mic dips into the scene as the old man is speaking.