In the Chinese dinner scene, Sheila's wine glass contains different amounts throughout the meal. At one point it's half full and then it's suddenly full.
After the play is finished, a stagehand comes into the dressing room to hand Corky the message from Mr. Guffman, then leaves the room. When he reads the message to the group, the stagehand is standing in the background over his shoulder. In the following shot when Corky sits down, she is gone again.