This is minimized script for reproduction: https://3v4l.org/dSB4T

<?php

class NonLeakingClass
{
}

//echo "Test empty object memory leakage" . PHP_EOL; // WARNING: Uncomment this line and PHP stops to leak memory on object creation, strange :)
for ($h = 0; $h < 5; $h++) {
    var_dump(memory_get_usage(false));
    $a = new NonLeakingClass();
    unset($a);
    gc_collect_cycles();
    var_dump(memory_get_usage(false));
}

exit;

According to debug data collected with the meminfo extension it seems that the problem is not actual memory leakage but instead the memory_get_usage function is not reporting correct number. Only experts on PHP's code would be able to tell what is the case.

This actually has nothing to do with the object construction, but rather with the var_dump(). Which is also why the first echo makes a difference.

PHP obviously lazily initializes some output mechanism.