When working with more complex XSL files, it can sometimes be useful to disable the Auto Map option. This can easily be achieved in the Auto Map Preferences popup you get when drawing lines in the design view of an XSL Map.
However, once disabled, you will not get this popup anymore to re-enable the Auto Map option. You need to do this through the Tools -> Preferences menu in JDeveloper. On the bottom of the list you see the XSL Maps menu with a submenu for Auto Map properties.
Here you can re-enable the Auto Map option for you XSL maps.