ownCloud (witch is based on SabreDAV) supports sync

conf/zpush/backend_caldav.php

@@ -11,8 +11,7 @@ define('CALDAV_PATH', '/caldav/calendars/%u/');
 define('CALDAV_PERSONAL', '');
 
 // If the CalDAV server supports the sync-collection operation
-// DAViCal and SOGo support it
 // Setting this to false will work with most servers, but it will be slower
-define('CALDAV_SUPPORTS_SYNC', false);
+define('CALDAV_SUPPORTS_SYNC', true);
 
 ?>

conf/zpush/backend_carddav.php

@@ -17,9 +17,8 @@ define('CARDDAV_CONTACTS_FOLDER_NAME', '%u Addressbook');
 
 
 // If the CardDAV server supports the sync-collection operation
-// DAViCal supports it, but SabreDav, Owncloud, SOGo don't
 // Setting this to false will work with most servers, but it will be slower: 1 petition for the href of vcards, and 1 petition for each vcard
-define('CARDDAV_SUPPORTS_SYNC', false);
+define('CARDDAV_SUPPORTS_SYNC', true);
 
 
 // If the CardDAV server supports the FN attribute for searches