Index: includes/ajax.inc
===================================================================
--- includes/ajax.inc	(revision 5)
+++ includes/ajax.inc	(working copy)
@@ -572,10 +572,7 @@ function ajax_pre_render_element($elemen
       case 'submit':
       case 'button':
       case 'image_button':
-        // Use the mousedown instead of the click event because form
-        // submission via pressing the enter key triggers a click event on
-        // submit inputs, inappropriately triggering AJAX behaviors.
-        $element['#ajax']['event'] = 'mousedown';
+        $element['#ajax']['event'] = 'click';
         // Attach an additional event handler so that AJAX behaviors
         // can be triggered still via keyboard input.
         $element['#ajax']['keypress'] = TRUE;