When Brenda meets Joe his French horn is in a different position almost every time the camera switches back to him, though he is not shown to be moving his arms at all.
When Claire is dancing with baby Maya after Ruth and George's wedding, Maya is wearing shoes/naked feet in no logical sequence.
At the end of season 3, Nate stumbles on Brenda's door beaten up. However, Nate was never informed of where Brenda's new house was.