--- kernel/classes/ezcontentobjecttreenode.php	2009-09-30 11:22:45.000000000 +0100
+++ kernel/classes/ezcontentobjecttreenode.php	2012-02-20 17:40:12.941592120 +0000
@@ -1596,7 +1596,7 @@
                                 $groupPermTempTable = $db->generateUniqueTempTableName( 'ezgroup_perm_tmp_%' );
                                 $sqlPermissionTempTables[] = $groupPermTempTable;
 
-                                $db->createTempTable( "CREATE TEMPORARY TABLE $groupPermTempTable ( user_id int )" );
+                                $db->createTempTable( "CREATE TEMPORARY TABLE $groupPermTempTable ( user_id int NOT NULL PRIMARY KEY )" );
                                 $db->query( "INSERT INTO $groupPermTempTable
                                                     SELECT DISTINCT contentobject_id AS user_id
                                                     FROM     ezcontentobject_tree