Index: wp-admin/js/nav-menu.dev.js
===================================================================
--- wp-admin/js/nav-menu.dev.js	(revision 14359)
+++ wp-admin/js/nav-menu.dev.js	(working copy)
@@ -379,10 +379,19 @@
 					}
 					
 					return false;
-				} else if ( e.target && e.target.className && -1 != e.target.className.indexOf('select-all') ) {
+				}
+				
+				// Toggle the select all
+				// @todo refactor, maybe use .toggle()
+				if ( 'select-all' == e.target.className ) {
 					var selectAreaMatch = /#(.*)$/.exec(e.target.href);
 					if ( selectAreaMatch && selectAreaMatch[1] ) {
-						$('#' + selectAreaMatch[1] + ' .tabs-panel-active input[type=checkbox]').attr('checked', 'checked');
+						
+						if ( $('#' + selectAreaMatch[1] + ' .tabs-panel-active input[type=checkbox]').attr('checked') )
+							$('#' + selectAreaMatch[1] + ' .tabs-panel-active input[type=checkbox]').attr('checked', false);
+						else
+							$('#' + selectAreaMatch[1] + ' .tabs-panel-active input[type=checkbox]').attr('checked', true);
+						
 						return false;
 					}
 				}