src/Pure/System/system_dialog.scala

--- a/src/Pure/System/system_dialog.scala	Sat Sep 07 15:10:33 2013 +0200
+++ b/src/Pure/System/system_dialog.scala	Sat Sep 07 15:28:16 2013 +0200
@@ -54,6 +54,7 @@
       case None =>
       case Some(window) =>
         window.visible = false
+        window.dispose
         _window = None
     }