diff --git a/plugins/calendar/drivers/kolab/kolab_calendar.php b/plugins/calendar/drivers/kolab/kolab_calendar.php
index 2fe072ab..49f8fa7d 100644
--- a/plugins/calendar/drivers/kolab/kolab_calendar.php
+++ b/plugins/calendar/drivers/kolab/kolab_calendar.php
@@ -346,7 +346,6 @@ class kolab_calendar
     if (!$old || PEAR::isError($old))
       return false;
 
-    $old['recurrence'] = '';  # clear old field, could have been removed in new, too
     $object = $this->_from_rcube_event($event, $old);
     $saved = $this->storage->save($object, 'event', $event['id']);
 
@@ -648,6 +647,11 @@ class kolab_calendar
 
     $event['_owner'] = $identity['email'];
 
+    # copy RDATE values as the UI doesn't yet support these
+    if (empty($event['recurrence']['FREQ']) && $old['recurrence']['RDATE'] && empty($old['recurrence']['FREQ'])) {
+      $event['recurrence']['RDATE'] = $old['recurrence']['RDATE'];
+    }
+
     // remove some internal properties which should not be saved
     unset($event['_savemode'], $event['_fromcalendar'], $event['_identity']);