Right at the beginning when Nora gets off the stage, she faints into a bench. Mark is standing right next to her. In the long shots Mark's coat is button to the very top. The close shots only the last button (hook) is closed.
When Nora is kissing Jude and screams when she sees Lucas approaching, she tears her dress so that Lucas will think Jude did it and perhaps kill Jude. In subsequent scenes, the dress is no longer torn.