Shorter test case:
<?php

class A{}
class B{}

for($i = 0; $i < 10; ++$i)
{
	$c = ['A','B'][rand() % 2];
	$t = eval("return new class extends $c{};");
	echo get_parent_class($t);
}

?>

It doesn't happen when the loop is unrolled:

<?php

$c = ['A','B'][rand() % 2];
$t = eval("return new class extends $c{};");
echo get_parent_class($t);
$c = ['A','B'][rand() % 2];
$t = eval("return new class extends $c{};");
echo get_parent_class($t);
....

?>
But it does happen if the eval is then wrapped in a function:

<?php
function make($c)
{
	return eval("return new class extends $c{};");
}
$c = ['A','B'][rand() % 2];
$t = make($c);
echo get_parent_class($t);
$c = ['A','B'][rand() % 2];
$t = make($c);
echo get_parent_class($t);
....
?>

Two identical make() functions:

<?php

class A{}
class B{}

function make1($c)
{
	return eval("return new class extends $c{};");
}

function make2($c)
{
	return eval("return new class extends $c{};");
}

echo get_parent_class(make1('A')); // Outputs A as expected
echo get_parent_class(make2('B')); // Outputs B as expected
echo get_parent_class(make1('B')); // Outputs A instead of B
echo get_parent_class(make2('A')); // Outputs B instead of A

?>

Duplicate of bug #73816.