When Count Danilo leaves Madame Sonia's residence after his romantic efforts are rejected, there is a closeup of him fully shutting the door. Next, when it cuts to a long shot of just Madame, the door is not fully closed but is in the process of swinging shut on its own.
When Sonia tears off a calendar sheet, it reads "Thursday, May III, 1885". However, May 3, 1885 was actually a Sunday.