Using FileMaker Advanced 13.0v3 on Windows 7, I ran a quick test. When I used the mouse to drag a table occurrence down past the bottom edge of the viewable area of the window, the window automatically scrolled down and the relationship map area enlarged--just as always has been the case.
Thank you PhilModJunk. Your answer is what I expected. This seems very strange to me. Now I am sure that there is a conflict with something else on my system that is causing this erratic behavior in FMP.