while doing a merge, I got some PHP errors. Seems like these steps fix the problem: 1. Change line 1215 of UnitOfWork.php to $id = $class->getIdentifierValue($document); it was ValueS before 2. in function _cascadeMerge starting in line 1464 of UnitOfWork.php change the inner calls from: $this->_cascadeMerge($relatedDocument, $visited); To: $this->_cascadeMerge($relatedDocument, $managedCopy, $visited); I didn't look deeper into ODM, just tried this to things and it seems to work now, so please excuse if it's bs ...