Lionel and Jean change sides of the bed they share as they were used to the "other side." When they actually do live together they sleep on the sides originally chose in this episode, which would be the "wrong" ones.
When Lionel first puts the plaster on top of the door frame, it's done lengthwise so as not to be so obvious. However, when Stephen notices it, it's perpendicular and hanging off the frame.
While cleaning up dishes in the kitchen, Jean says "It's my disherwasher ".