Flushing more than once causes a warning. Resetting $_collections to the initial state avoids it.

Author: thirsch

lib/Doctrine/Hydrator/RecordDriver.php

@@ -118,7 +118,7 @@ public function flush()
             $coll->takeSnapshot();
         }
         $this->_initializedRelations = null;
-        $this->_collections = null;
+        $this->_collections = array();
         $this->_tables = null;
     }
 }