This is in the second episode, "In God, And Nobody Else, We Trust", almost at the end during the Luau scene:

Gidget's sister Anne arrives at the Luau looking for her husband. She passes Treasure Chest, who is walking away from the Luau and into the woods(which Anne has just come out of). Anne stops her and the two talk for a minute before Anne turns and scans the crowd looking for John. The camera pans across the kids dancing before cutting back to Anne. Problem is, Treasure, who Anne had just turned and walked away from, is seen dancing with the other kids during the pan-cut, even though she should be in the woods.