When a project is closed in the left hand panel, any tabs for sheets contained by that project that are still open in the Editor window stay open. What is dangerous is that not only are the tabs still open, it is still possible to edit the sheets in these tabs and to save the results to the project that the user may think is now closed and locked against further savings. I think it would be safer if when closing a project in the left hand panel, it should check for any opened sheets and, if all project sheets are closed then just close the project but if any are still open then pop up a message to say: "Please save then close all opened sheets in this project before trying to close the project again." Or maybe check to see of all opened sheets are closed and close the project only if they are all saved otherwise pop up a message to say: "Please save all opened sheets in this project before trying to close the project again."