My main subview shows an arc across three FK relationships, but when I add those same tables to another subview involving all four tables, the arc doesn't appear, and it's not obvious how to make it appear.
I reselected the objects in the main subview and created a new subview from them, and the arc appears. But in the original subview that didn't have the arc there doesn't appear to be any option to show it.
SQL Developer 4.0.2.15 build 15.21 on Win7 Pro