Continuity mistake: The buildings seen from the window of Rob's office change in different episodes.
Continuity mistake: The number of glass "pea pod" shaped sphere balls change through out the series. In "Don't Trip Over That Mountain" there were only 3 spheres. In several episodes there were 4 spheres and in others there were 5 of them.
Continuity mistake: Every 4 episodes the table in the living room changes completely, one episode it's a huge oval table, in another it's a medium-sized round table, in another episode it turns into a very small round table, some times it's even a large egg shape.