There is a problem with sqlnavigator since version 7.1 and perhaps earlier that is present in 7.2. The issue is reproducable but you have to follow the exact steps.
Open sqlnavigator and open a session (a new sql editor appears)
Choose job scheduler using tools menu.
Click and go to the initial sql editor
Click and go the scheduler window again
Click and go to the initial sql editor again.
You will notice that common functions like find text, paste, cut, insert dbms_output and many more are grayed in edit and search menu and keyboard shortcuts do not work either. These features are lost in any sql editor in any session (even new editors) until the scheduler window is closed