In metacity-2.4.34/src/delete.c, in function meta_window_delete () the 
code looks like this (in particular, note the comment in the 
window->has_focus case) 
 
  if (window->delete_window) 
    { 
      meta_topic (META_DEBUG_WINDOW_OPS, 
                  "Deleting %s with delete_window request\n", 
                  window->desc); 
      meta_window_send_icccm_message (window, 
                                      window->display->atom_wm_delete_window, 
                                      timestamp); 
    }                                  
[...]                                  
  if (window->has_focus)               
    { 
      /* This is unfortunately going to result in weirdness 
       * if the window doesn't respond to the delete event. 
       * I don't know how to avoid that though. 
       */ 
      meta_topic (META_DEBUG_FOCUS, 
                  "Focusing top window because focus window %s was 
deleted/killed\n", 
                  window->desc); 
      meta_screen_focus_top_window (window->screen, window); 
    }  
 
 
If a user tries to close the window and the window denies the request to be 
closed (e.g. a JFrame that has its close operation set to the 
DO_NOTHING_ON_CLOSE), the focus is still switced to some other window. 
 
See sun Bug Id 4877726: 
http://developer.java.sun.com/developer/bugParade/bugs/4877726.html