diff -u b/core/misc/ajax.js b/core/misc/ajax.js
--- b/core/misc/ajax.js
+++ b/core/misc/ajax.js
@@ -648,7 +648,6 @@
     // There is no simple way to know which submission mechanism will be used,
     // so we add to extraData regardless, and allow it to be ignored in the
     // former case.
-    this.hiddenCopy = null;
     if (this.$form) {
       options.extraData = options.extraData || {};
 
@@ -659,18 +658,12 @@
 
       // The triggering element is about to be disabled (see below), but if it
       // contains a value (e.g., a checkbox, textfield, select, etc.), ensure
-      // value is included in all submissions. As per above, submissions that use
-      // $.ajax() are already serialized prior to the element being disabled.
-      // However, that does not handle IFRAME submissions, nor does it handle any
-      // subsequent submissions that may happen before this ajax request is
-      // complete. To cover these cases, create a hidden version of the input
-      // field, that is deleted when the request is complete.
+      // that value is included in the submission. As per above, submissions
+      // that use $.ajax() are already serialized prior to the element being
+      // disabled, so this is only needed for IFRAME submissions.
       var v = $.fieldValue(this.element);
       if (v !== null) {
-        this.hiddenCopy = $('<input type="hidden" />')
-          .attr('name', this.element.name)
-          .val(Drupal.checkPlain(v));
-        $(this.element).after(this.hiddenCopy);
+        options.extraData[this.element.name] = v;
       }
     }
 
@@ -740,10 +733,6 @@
     if (this.progress.object) {
       this.progress.object.stopMonitoring();
     }
-    // Remove the hidden version of the input element.
-    if (this.hiddenCopy) {
-      $(this.hiddenCopy).remove();
-    }
     $(this.element).prop('disabled', false);
 
     // Save element's ancestors tree so if the element is removed from the dom
@@ -772,6 +761,7 @@
     // There is no simple way to know which submission mechanism will be used,
     // so we add to extraData regardless, and allow it to be ignored in the
     // former case.
+    this.hiddenCopy = null;
     if (this.$form) {
       options.extraData = options.extraData || {};
 
@@ -782,12 +772,18 @@
 
       // The triggering element is about to be disabled (see below), but if it
       // contains a value (e.g., a checkbox, textfield, select, etc.), ensure
-      // that value is included in the submission. As per above, submissions
-      // that use $.ajax() are already serialized prior to the element being
-      // disabled, so this is only needed for IFRAME submissions.
+      // value is included in all submissions. As per above, submissions that
+      // use $.ajax() are already serialized prior to the element being
+      // disabled. However, that does not handle IFRAME submissions, nor does
+      // it handle any subsequent submissions that may happen before this ajax
+      // request is complete. To cover these cases, create a hidden version of
+      // the input field, that is deleted when the request is complete.
       var v = $.fieldValue(this.element);
       if (v !== null) {
-        options.extraData[this.element.name] = v;
+        this.hiddenCopy = $('<input type="hidden" />')
+          .attr('name', this.element.name)
+          .val(Drupal.checkPlain(v));
+        $(this.element).after(this.hiddenCopy);
       }
     }
 
@@ -841,10 +837,6 @@
     if (this.progress.object) {
       this.progress.object.stopMonitoring();
     }
-    // Remove the hidden version of the input element.
-    if (this.hiddenCopy) {
-      $(this.hiddenCopy).remove();
-    }
     // Undo hide.
     $(this.wrapper).show();
     // Re-enable the element.
@@ -863,6 +855,10 @@
     if (this.progress.object) {
       this.progress.object.stopMonitoring();
     }
+    // Remove the hidden version of the input element.
+    if (this.hiddenCopy) {
+      $(this.hiddenCopy).remove();
+    }
     $(this.element).prop('disabled', false);
 
     // Save element's ancestors tree so if the element is removed from the dom
@@ -968,6 +964,10 @@
     if (this.progress.object) {
       this.progress.object.stopMonitoring();
     }
+    // Remove the hidden version of the input element.
+    if (this.hiddenCopy) {
+      $(this.hiddenCopy).remove();
+    }
     // Undo hide.
     $(this.wrapper).show();
     // Re-enable the element.