cakephp's memory leak iterating over find

    $registros = $source_table->find()->order('id');
		$inicio = time();
		$diff = time();
		foreach ($registros as $registro) {
		//for ($n = 0; $n < 500000; $n++) { //<-------------- see the difference when iterating over a for(0..500k) than over a foreach($registros)
			$num++;

			if ($num % 100 == 0) {
				$memoria_usada = number_format(memory_get_usage(true), 0);
				$to_log = __("used memory: ".$memoria_usada."\t$num records processed (time ".(time() - $inicio)."; diff: ".(time() - $diff).")");
				Log::info($to_log,'memory');
				$diff = time();
			}
		}

$sourcetable is a table with 58k records