Ticket #20857: 20857.2.diff

wp-admin/js/common.dev.js

@@ -189 +189 @@
                 over: function(e){
                         var b, h, o, f, m = $(this).find('.wp-submenu'), menutop, wintop, maxtop;
 
+                        if ( m.is(':visible') )
+                                return;
+
                         menutop = $(this).offset().top;
                         wintop = $(window).scrollTop();
                         maxtop = menutop - wintop - 30; // max = make the top of the sub almost touch admin bar