When you use the ER Diagram properties to create a new ER Diagram under a Subject Area, there is a checkbox choice to 'Automatically Populate From Subject Area'. When you choose that option, all the model objects are dumped one on top of the other. Should the layout in the new diagram not be the same as the diagram being viewed?
Each new ER Diagram has a unique display. The Automatically Populate From Subject Area is working as designed. However, the Diagram layout will be maintained if you copy and paste the objects from the (Source) ER Diagram to a new (Target) ER Diagram. Alternatively, when the overlapping of model object occurs, you can use five diagram layout options to lay them out accordingly.