Create a new document, type in some text, then do "Save As".  In the popup window, give a file name, select "auto detect" associated with character encoding, then press "Save".  The behaviour then seems normal - a message at the status bar at the bottom says "saving somefilename ...", but actually nothing happens.  If it is a modified or new file, Gedit will prompt for whether to save changes at the time of quitting Gedit.  But the serious thing is when the file has not been edited and just saved to a new file name or location, it does not even warn that it is not saved when quit.