diff --git a/src/applications/maniphest/editor/ManiphestEditEngine.php b/src/applications/maniphest/editor/ManiphestEditEngine.php
--- a/src/applications/maniphest/editor/ManiphestEditEngine.php
+++ b/src/applications/maniphest/editor/ManiphestEditEngine.php
@@ -60,10 +60,6 @@
 
     $priority_map = ManiphestTaskPriority::getTaskPriorityMap();
 
-    // TODO: Restore these or toss them:
-    // - When closing an unassigned task, assign the closing user.
-    // - Make sure implicit CCs on actions are working reasonably.
-
     if ($object->isClosed()) {
       $priority_label = null;
       $owner_label = null;
diff --git a/src/applications/maniphest/editor/ManiphestTransactionEditor.php b/src/applications/maniphest/editor/ManiphestTransactionEditor.php
--- a/src/applications/maniphest/editor/ManiphestTransactionEditor.php
+++ b/src/applications/maniphest/editor/ManiphestTransactionEditor.php
@@ -745,5 +745,31 @@
     return $errors;
   }
 
+  protected function expandTransaction(
+    PhabricatorLiskDAO $object,
+    PhabricatorApplicationTransaction $xaction) {
+
+    $results = parent::expandTransaction($object, $xaction);
+
+    switch ($xaction->getTransactionType()) {
+      case ManiphestTransaction::TYPE_OWNER:
+        // When a task is reassigned, move the old owner to the subscriber
+        // list so they're still in the loop.
+        $owner_phid = $object->getOwnerPHID();
+        if ($owner_phid) {
+          $results[] = id(new ManiphestTransaction())
+            ->setTransactionType(PhabricatorTransactions::TYPE_SUBSCRIBERS)
+            ->setIgnoreOnNoEffect(true)
+            ->setNewValue(
+              array(
+                '+' => array($owner_phid => $owner_phid),
+              ));
+        }
+        break;
+    }
+
+    return $results;
+  }
+
 
 }