Description:
------------
In php versions 7.0.6, 5.6.22, 5.6.16, 5.4.35
I have construct object that have anonymous function in his field named "callback".
When i am trying to unset object - object is still exists, memory that allocated to object is not released.
In php version 5.3.10 memory is released.

Test script:
---------------
<?php
class Leak
{
    protected $callback;

    public function set()
    {
        $this->callback = function(){};
    }
}
$base_usage = memory_get_usage();
for($i=0;$i<12;$i++) {
    echo 'step-1 ' . (memory_get_usage() - $base_usage) . PHP_EOL;
    $leak = new Leak();
    $leak->set();
    unset($leak);
    echo 'step-2 ' . (memory_get_usage() - $base_usage) . PHP_EOL;
}
echo 'step-3 ' . (memory_get_usage() - $base_usage) . PHP_EOL;

Expected result:
----------------
step-1 344
step-2 840
step-1 840
step-2 840
step-1 840
step-2 840
step-1 840
step-2 840
step-1 840
step-2 840
step-1 840
....

Actual result:
--------------
step-1 344
step-2 840
step-1 840
step-2 1328
step-1 1328
step-2 1816
step-1 1816
step-2 2304
step-1 2304
step-2 2792
step-1 2792
step-2 3280
....