diff --git a/src/applications/calendar/editor/PhabricatorCalendarEventEditEngine.php b/src/applications/calendar/editor/PhabricatorCalendarEventEditEngine.php
--- a/src/applications/calendar/editor/PhabricatorCalendarEventEditEngine.php
+++ b/src/applications/calendar/editor/PhabricatorCalendarEventEditEngine.php
@@ -164,6 +164,8 @@
 
     if ($this->getIsCreate() || $object->getIsRecurring()) {
       $fields[] = id(new PhabricatorEpochEditField())
+        ->setIsLockable(false)
+        ->setIsDefaultable(false)
         ->setAllowNull(true)
         ->setKey('until')
         ->setLabel(pht('Repeat Until'))
@@ -189,6 +191,8 @@
     $fields[] = id(new PhabricatorEpochEditField())
       ->setKey('start')
       ->setLabel(pht('Start'))
+      ->setIsLockable(false)
+      ->setIsDefaultable(false)
       ->setTransactionType(
         PhabricatorCalendarEventStartDateTransaction::TRANSACTIONTYPE)
       ->setDescription(pht('Start time of the event.'))
@@ -199,6 +203,8 @@
     $fields[] = id(new PhabricatorEpochEditField())
       ->setKey('end')
       ->setLabel(pht('End'))
+      ->setIsLockable(false)
+      ->setIsDefaultable(false)
       ->setTransactionType(
         PhabricatorCalendarEventEndDateTransaction::TRANSACTIONTYPE)
       ->setDescription(pht('End time of the event.'))
diff --git a/src/applications/transactions/storage/PhabricatorEditEngineConfiguration.php b/src/applications/transactions/storage/PhabricatorEditEngineConfiguration.php
--- a/src/applications/transactions/storage/PhabricatorEditEngineConfiguration.php
+++ b/src/applications/transactions/storage/PhabricatorEditEngineConfiguration.php
@@ -128,6 +128,9 @@
 
     $values = $this->getProperty('defaults', array());
     foreach ($fields as $key => $field) {
+      if (!$field->getIsDefaultable()) {
+        continue;
+      }
       if ($is_new) {
         if (array_key_exists($key, $values)) {
           $field->readDefaultValueFromConfiguration($values[$key]);
@@ -157,6 +160,11 @@
       }
     }
 
+    // If the field isn't lockable, remove any lock we applied.
+    if (!$field->getIsLockable()) {
+      $field->setIsLocked(false);
+    }
+
     $fields = $this->reorderFields($fields);
 
     $preamble = $this->getPreamble();