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();
			}
		}

the foreach: see how the memory usage increases
2017-02-11 05:36:57 Info: used memory: 128,712,704 32000 records processed (time 5; diff: 0)
2017-02-11 05:36:57 Info: used memory: 130,809,856 32100 records processed (time 5; diff: 0)
2017-02-11 05:36:57 Info: used memory: 130,809,856 32200 records processed (time 5; diff: 0)
2017-02-11 05:36:57 Info: used memory: 130,809,856 32300 records processed (time 5; diff: 0)
2017-02-11 05:36:57 Info: used memory: 130,809,856 32400 records processed (time 5; diff: 0)
2017-02-11 05:36:57 Info: used memory: 130,809,856 32500 records processed (time 5; diff: 0)
2017-02-11 05:36:57 Info: used memory: 132,907,008 32600 records processed (time 5; diff: 0)
2017-02-11 05:36:57 Info: used memory: 132,907,008 32700 records processed (time 5; diff: 0)
2017-02-11 05:36:57 Info: used memory: 132,907,008 32800 records processed (time 5; diff: 0)
2017-02-11 05:36:57 Info: used memory: 132,907,008 32900 records processed (time 5; diff: 0)
2017-02-11 05:36:57 Info: used memory: 132,907,008 33000 records processed (time 5; diff: 0)
2017-02-11 05:36:57 Info: used memory: 132,907,008 33100 records processed (time 5; diff: 0)
2017-02-11 05:36:57 Info: used memory: 132,907,008 33200 records processed (time 5; diff: 0)

the for:
....
2017-02-11 05:36:01 Info: used memory: 13,369,344 498800 records processed (time 45; diff: 0)
2017-02-11 05:36:01 Info: used memory: 13,369,344 498900 records processed (time 45; diff: 0)
2017-02-11 05:36:01 Info: used memory: 13,369,344 499000 records processed (time 45; diff: 0)
2017-02-11 05:36:01 Info: used memory: 13,369,344 499100 records processed (time 45; diff: 0)
2017-02-11 05:36:01 Info: used memory: 13,369,344 499200 records processed (time 45; diff: 0)
2017-02-11 05:36:01 Info: used memory: 13,369,344 499300 records processed (time 45; diff: 0)
2017-02-11 05:36:01 Info: used memory: 13,369,344 499400 records processed (time 45; diff: 0)
2017-02-11 05:36:01 Info: used memory: 13,369,344 499500 records processed (time 45; diff: 0)
2017-02-11 05:36:01 Info: used memory: 13,369,344 499600 records processed (time 45; diff: 0)
2017-02-11 05:36:01 Info: used memory: 13,369,344 499700 records processed (time 45; diff: 0)
2017-02-11 05:36:01 Info: used memory: 13,369,344 499800 records processed (time 45; diff: 0)
2017-02-11 05:36:01 Info: used memory: 13,369,344 499900 records processed (time 45; diff: 0)
2017-02-11 05:36:01 Info: used memory: 13,369,344 500000 records processed (time 45; diff: 0)

$sourcetable is a table with 58k records