diff --git a/lib/kolab_sync_data.php b/lib/kolab_sync_data.php
--- a/lib/kolab_sync_data.php
+++ b/lib/kolab_sync_data.php
@@ -490,7 +490,23 @@
      */
     public function createEntry($folderId, Syncroton_Model_IEntry $entry)
     {
-        $entry = $this->toKolab($entry, $folderId);
+        // If we don't have an existing event (not a modification) we nevertheless check for conflicts.
+        // This is necessary so we don't overwrite the server-side copy in case the client did not have it available
+        // when generating an Add command.
+        $existing = null;
+        try {
+            $foldername = $this->getFolderName($folderId);
+            $folder = $this->getFolderObject($foldername);
+            $existing = $folder->get_object($entry->uID);
+
+            if ($existing) {
+                $this->logger->debug('Found and existing entry for UID: ' . $entry->uID);
+            }
+        } catch (Exception $e) {
+            // uID is not available on exceptions, so we guard for that and silently ignore.
+        }
+
+        $entry = $this->toKolab($entry, $folderId, $existing);
         $entry = $this->createObject($folderId, $entry);
 
         if (empty($entry)) {