diff --git a/resources/celerity/map.php b/resources/celerity/map.php
--- a/resources/celerity/map.php
+++ b/resources/celerity/map.php
@@ -13,7 +13,7 @@
     'core.pkg.js' => 'd2de90d9',
     'dark-console.pkg.js' => '187792c2',
     'differential.pkg.css' => 'ffb69e3d',
-    'differential.pkg.js' => '8deec4cd',
+    'differential.pkg.js' => 'e31329dc',
     'diffusion.pkg.css' => '42c75c37',
     'diffusion.pkg.js' => '78c9885d',
     'maniphest.pkg.css' => '35995d6d',
@@ -473,7 +473,7 @@
     'rsrc/js/core/behavior-copy.js' => 'cf32921f',
     'rsrc/js/core/behavior-detect-timezone.js' => '78bc5d94',
     'rsrc/js/core/behavior-device.js' => 'ac2b1e01',
-    'rsrc/js/core/behavior-drag-and-drop-textarea.js' => '7ad020a5',
+    'rsrc/js/core/behavior-drag-and-drop-textarea.js' => '7df68a45',
     'rsrc/js/core/behavior-fancy-datepicker.js' => '36821f8d',
     'rsrc/js/core/behavior-form.js' => '55d7b788',
     'rsrc/js/core/behavior-gesture.js' => 'b58d1a2a',
@@ -589,7 +589,7 @@
     'javelin-behavior-aphlict-listen' => '4e61fa88',
     'javelin-behavior-aphlict-status' => 'c3703a16',
     'javelin-behavior-aphront-basic-tokenizer' => '3b4899b0',
-    'javelin-behavior-aphront-drag-and-drop-textarea' => '7ad020a5',
+    'javelin-behavior-aphront-drag-and-drop-textarea' => '7df68a45',
     'javelin-behavior-aphront-form-disable-on-submit' => '55d7b788',
     'javelin-behavior-aphront-more' => '506aa3f4',
     'javelin-behavior-audio-source' => '3dc5ad43',
@@ -1604,12 +1604,6 @@
       'javelin-install',
       'javelin-dom',
     ),
-    '7ad020a5' => array(
-      'javelin-behavior',
-      'javelin-dom',
-      'phabricator-drag-and-drop-file-upload',
-      'phabricator-textareautils',
-    ),
     '7b139193' => array(
       'javelin-behavior',
       'javelin-stratcom',
@@ -1620,6 +1614,13 @@
       'javelin-install',
       'javelin-dom',
     ),
+    '7df68a45' => array(
+      'javelin-behavior',
+      'javelin-dom',
+      'javelin-json',
+      'phabricator-drag-and-drop-file-upload',
+      'phabricator-textareautils',
+    ),
     '80bff3af' => array(
       'javelin-install',
       'javelin-typeahead-source',
diff --git a/src/view/form/control/PhabricatorRemarkupControl.php b/src/view/form/control/PhabricatorRemarkupControl.php
--- a/src/view/form/control/PhabricatorRemarkupControl.php
+++ b/src/view/form/control/PhabricatorRemarkupControl.php
@@ -6,6 +6,7 @@
   private $disableFullScreen = false;
   private $canPin;
   private $sendOnEnter = false;
+  private $remarkupMetadata = array();
 
   public function setDisableMacros($disable) {
     $this->disableMacro = $disable;
@@ -35,6 +36,15 @@
     return $this->sendOnEnter;
   }
 
+  public function setRemarkupMetadata(array $value) {
+    $this->remarkupMetadata = $value;
+    return $this;
+  }
+
+  public function getRemarkupMetadata() {
+    return $this->remarkupMetadata;
+  }
+
   protected function renderInput() {
     $id = $this->getID();
     if (!$id) {
@@ -47,6 +57,25 @@
       throw new PhutilInvalidStateException('setUser');
     }
 
+    // NOTE: Metadata is passed to Javascript in a structured way, and also
+    // dumped directly into the form as an encoded string. This makes it less
+    // likely that we'll lose server-provided metadata (for example, from a
+    // saved draft) if there is a client-side error.
+
+    $metadata_name = $this->getName().'_metadata';
+    $metadata_value = (object)$this->getRemarkupMetadata();
+    $metadata_string = phutil_json_encode($metadata_value);
+
+    $metadata_id = celerity_generate_unique_node_id();
+    $metadata_input = phutil_tag(
+      'input',
+      array(
+        'type' => 'hidden',
+        'id' => $metadata_id,
+        'name' => $metadata_name,
+        'value' => $metadata_string,
+      ));
+
     // We need to have this if previews render images, since Ajax can not
     // currently ship JS or CSS.
     require_celerity_resource('phui-lightbox-css');
@@ -56,6 +85,8 @@
         'aphront-drag-and-drop-textarea',
         array(
           'target' => $id,
+          'remarkupMetadataID' => $metadata_id,
+          'remarkupMetadataValue' => $metadata_value,
           'activatedClass' => 'aphront-textarea-drag-and-drop',
           'uri' => '/file/dropupload/',
           'chunkThreshold' => PhabricatorFileStorageEngine::getChunkThreshold(),
@@ -353,6 +384,7 @@
       array(
         $buttons,
         parent::renderInput(),
+        $metadata_input,
       ));
   }
 
diff --git a/webroot/rsrc/js/core/behavior-drag-and-drop-textarea.js b/webroot/rsrc/js/core/behavior-drag-and-drop-textarea.js
--- a/webroot/rsrc/js/core/behavior-drag-and-drop-textarea.js
+++ b/webroot/rsrc/js/core/behavior-drag-and-drop-textarea.js
@@ -2,6 +2,7 @@
  * @provides javelin-behavior-aphront-drag-and-drop-textarea
  * @requires javelin-behavior
  *           javelin-dom
+ *           javelin-json
  *           phabricator-drag-and-drop-file-upload
  *           phabricator-textareautils
  */
@@ -10,6 +11,21 @@
 
   var target = JX.$(config.target);
 
+  var metadata_node = JX.$(config.remarkupMetadataID);
+  var metadata_value = config.remarkupMetadataValue;
+
+  function set_metadata(key, value) {
+    metadata_value[key] = value;
+    metadata_node.value = JX.JSON.stringify(metadata_value);
+  }
+
+  function get_metadata(key, default_value) {
+    if (metadata_value.hasOwnProperty(key)) {
+      return metadata_value[key];
+    }
+    return default_value;
+  }
+
   if (JX.PhabricatorDragAndDropFileUpload.isSupported()) {
     var drop = new JX.PhabricatorDragAndDropFileUpload(target)
       .setURI(config.uri)