src/java.desktop/share/classes/java/awt/Desktop.java

*** 1000,1009 ****
--- 1000,1018 ----
       * @since 9
       */
      public void setDefaultMenuBar(final JMenuBar menuBar) {
          checkEventsProcessingPermission();
          checkActionSupport(Action.APP_MENU_BAR);
+ 
+         if (menuBar != null) {
+             Container parent = menuBar.getParent();
+             if (parent != null) {
+                 parent.remove(menuBar);
+                 menuBar.updateUI();
+             }
+         }
+ 
          peer.setDefaultMenuBar(menuBar);
      }
  
      /**
       * Opens a folder containing the {@code file} and selects it