Jazz wears regular glasses when he enters the house, but is wearing his trademark shades in the shot of him getting thrown out (a piece of often-reused footage.)
During the birthday party, the forks on the hassock change position between shots.
When Will is viewing the apartment with Mr. Clark, you can clearly see that the view from the window (sunset, palm trees) is actually a backdrop as the floor of the studio is visible outside the window.
It is indicated that Ashley is not supposed to drink champagne, however all the adults have their own glasses, meaning Geoffrey prepared a glass for Ashley even though she is underage.