It's a bit of an odd thing, but toward the beginning of the episode, when Arthur is in the kitchen with his tux on, Carrie comes into the kitchen and the camera angle exposes the kitchen has an open wall that has a space carved out of it. It looks like a shooting/editing error.
As Doug and Carrie are waiting to greet the bride and groom, the musician playing the blue guitar is moving and grooving apparently to another song. His motions don't match the music. He also changes chords not in synch to the music.