Description:
------------
It's reproducible on all php >= 7 versions (including 7.4-rc)

I probably am missing something, but I cannot find it documented anywhere, hence the behaviour surprises me.

Test script:
---------------
<?php

$files = iterator_to_array(new DirectoryIterator(__DIR__));
var_dump($files[0]->getRealPath());

foreach (new DirectoryIterator(__DIR__) as $f) {
    var_dump($f->getRealPath());
    break;
}

Expected result:
----------------
string(4) "/app"
string(4) "/app"

Actual result:
--------------
bool(false)
string(4) "/app"