Index: includes/ajax.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/ajax.inc,v
retrieving revision 1.40
diff -u -p -r1.40 ajax.inc
--- includes/ajax.inc	17 Dec 2010 01:03:58 -0000	1.40
+++ includes/ajax.inc	22 Dec 2010 14:32:19 -0000
@@ -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;
Index: misc/ajax.js
===================================================================
RCS file: /cvs/drupal/drupal/misc/ajax.js,v
retrieving revision 1.34
diff -u -p -r1.34 ajax.js
--- misc/ajax.js	21 Dec 2010 04:21:16 -0000	1.34
+++ misc/ajax.js	22 Dec 2010 15:36:25 -0000
@@ -149,11 +149,9 @@ Drupal.ajax = function (base, element, e
       return ajax.beforeSerialize(element_settings, options);
     },
     beforeSubmit: function (form_values, element_settings, options) {
-      ajax.ajaxing = true;
       return ajax.beforeSubmit(form_values, element_settings, options);
     },
     beforeSend: function (xmlhttprequest) {
-      ajax.ajaxing = true;
       return ajax.beforeSend(xmlhttprequest, ajax.options);
     },
     success: function (response, status) {
@@ -176,6 +174,31 @@ Drupal.ajax = function (base, element, e
 
   // Bind the ajaxSubmit function to the element event.
   $(ajax.element).bind(element_settings.event, function (event) {
+    // Do not perform another ajax command if one is already in progress.
+    if (ajax.ajaxing) {
+      return false;
+    }
+    // Retrieve the actual element, on which the event was triggered. Normally,
+    // browsers provide the actual source element that triggered the event in
+    // event.target, resp., event.currentElement. But if a 'click' event is
+    // bound to a form button and enter is pressed in a text input, a browser
+    // will submit the form and therefore trigger the click event of the form
+    // button. Therefore, we need to figure out the original source element.
+    // Clicking a button does not provide an originalEvent.
+    event.ajaxSrcElement = null;
+    if (event.originalEvent) {
+      event.ajaxSrcElement = event.originalEvent.explicitOriginalTarget || event.originalEvent.relatedTarget;
+    }
+    // Also try the browser-specific (but also HTML5) activeElement property,
+    // denoting the focused form element.
+    event.ajaxSrcElement = event.ajaxSrcElement || document.activeElement;
+    // Some browsers may return text nodes; use the parentNode instead.
+    event.ajaxSrcElement = (event.ajaxSrcElement.nodeType == 1 ? event.ajaxSrcElement : event.ajaxSrcElement.parentNode);
+    // If we found the source and it is not the bound element, cancel.
+    if (event.ajaxSrcElement && event.ajaxSrcElement != ajax.element) {
+      return;
+    }
+    ajax.ajaxing = true;
     return ajax.eventResponse(this, event);
   });
 
@@ -183,7 +206,7 @@ Drupal.ajax = function (base, element, e
   // can be triggered through keyboard input as well as e.g. a mousedown
   // action.
   if (element_settings.keypress) {
-    $(element_settings.element).keypress(function (event) {
+    $(ajax.element).keypress(function (event) {
       return ajax.keypressResponse(this, event);
     });
   }
@@ -208,7 +231,7 @@ Drupal.ajax.prototype.keypressResponse =
   // spacebar activation causes inappropriate activation if #ajax['keypress'] is 
   // TRUE. On a text-type widget a space should always be a space.
   if (event.which == 13 || (event.which == 32 && element.type != 'text' && element.type != 'textarea')) {
-    $(ajax.element_settings.element).trigger(ajax.element_settings.event);
+    $(ajax.element).trigger(ajax.element_settings.event);
     return false;
   }
 };
@@ -225,11 +248,6 @@ Drupal.ajax.prototype.eventResponse = fu
   // Create a synonym for this to reduce code confusion.
   var ajax = this;
 
-  // Do not perform another ajax command if one is already in progress.
-  if (ajax.ajaxing) {
-    return false;
-  }
-
   try {
     if (ajax.form) {
       // If setClick is set, we must set this to ensure that the button's