understanding php memory GC with same var

gistfile1.php

<?php
$loader = include __DIR__ . '/../vendor/autoload.php';
$loop = React\EventLoop\Factory::create();

$counter = 0;
$timer = $loop->addPeriodicTimer(10, function() use(&$timer, &$counter) {

    $counter++;

    if ($counter > 1 && $counter <= 5) {
        $queue = [];

        for ($i = 0; $i < 100000; $i++) {
            $o = new stdClass();
            $queue[] = $o;
        }
        unset($queue);
    }

    echo
        'Counter: ' . $counter . "\n" .
        'Memory: ' . round(memory_get_usage() / 1024 / 1024, 2) . " MB\n" .
        'Memory True: ' . round(memory_get_usage(true) / 1024 / 1024, 2) . " MB\n" .
        'Peak Memory: ' . round(memory_get_peak_usage() / 1024 / 1024, 2) . "MB \n" .
        'Peak Memory True : ' . round(memory_get_peak_usage(true) / 1024 / 1024, 2) . "MB \n" . "\n\n";

    if ($counter > 10)
        die;
});

$loop->run();

/** outputs **/

Counter: 10
Memory: 8.23 MB
Memory True: 9.25 MB
Peak Memory: 26.86MB
Peak Memory True : 27.5MB


Counter: 11
Memory: 8.23 MB
Memory True: 9.25 MB
Peak Memory: 26.86MB
Peak Memory True : 27.5MB