Index: typo3/sysext/backend/Classes/Form/FormDataProvider/AbstractItemProvider.php
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- typo3/sysext/backend/Classes/Form/FormDataProvider/AbstractItemProvider.php	(revision )
+++ typo3/sysext/backend/Classes/Form/FormDataProvider/AbstractItemProvider.php	(revision )
@@ -970,7 +970,14 @@
                         // "field1###' AND ..." -> array("field1", "' AND ...")
                         $whereClauseSubParts = explode('###', $value, 2);
                         // @todo: Throw exception if there is no value? What happens for NEW records?
+                        if (array_key_exists($whereClauseSubParts[0], $result['databaseRow'])){
-                        $rowFieldValue = $result['databaseRow'][$whereClauseSubParts[0]];
+                            $rowFieldValue = $result['databaseRow'][$whereClauseSubParts[0]];
+                        } else if (array_key_exists('flexParentDatabaseRow', $result)){
+                            $rowFieldValue = $result['flexParentDatabaseRow'][$whereClauseSubParts[0]];
+                        } else {
+                            $rowFieldValue = null;
+                        }
+
                         if (is_array($rowFieldValue)) {
                             // If a select or group field is used here, it may have been processed already and
                             // is now an array. Use first selected value in this case.