Is this a bug in PHP? Running execute.php on Ubuntu with PHP 5.5.4 executes successfully, but on CentOS with same PHP version it gives Fatal error.

execute.php

<?php

// Autoloader that does not need subdirectories (because Gist does not support subdirectories).
// Same thing happens with default SPL autoloader where namespaced files are in subdirectories.
spl_autoload_register(
    function($class) {
        spl_autoload(str_replace("\\", "_", $class));
    }
);

$bar = new Some\Bar();

$foo = new Some\Foo();
$foo->bar($bar);

other_bar.php

<?php

namespace Other;

class Bar {
    public function baz() {
        echo "self: " . get_class($this) . "\n";
    }
}

some_bar.php

<?php

namespace Some;

use Other\Bar as OtherBar;

class Bar extends OtherBar {
    public function baz() {
        echo "self: " . get_class($this) . "\n";
        echo "parent: " . get_parent_class($this) . "\n";
    }
}

some_foo.php

<?php

namespace Some;

use Other\Bar;

class Foo {
    public function bar(Bar $bar) {
        $bar->baz();
    }
}

Seems like the culprit is OPcache:

$ php -v      
PHP 5.5.9-1+sury.org~saucy+1 (cli) (built: Feb 13 2014 15:58:58) 
Copyright (c) 1997-2014 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2014 Zend Technologies
    with Zend OPcache v7.0.3, Copyright (c) 1999-2014, by Zend Technologies
    with Xdebug v2.2.3, Copyright (c) 2002-2013, by Derick Rethans

$ php -i | grep opcache.enable_cli
opcache.enable_cli => On => On

$ php execute.php                 
self: Some\Bar
parent: Other\Bar

$ sudo nano /etc/php5/cli/php.ini 

$ php -i | grep opcache.enable_cli
opcache.enable_cli => Off => Off

$ php execute.php                 

Fatal error: Cannot use Other\Bar as Bar because the name is already in use 
in /tmp/path/some_foo.php on line 5

Call Stack:
    0.0005     234520   1. {main}() /tmp/path/execute.php:0
    0.0036     241464   2. spl_autoload_call() /tmp/path/execute.php:13
    0.0036     241496   3. {closure:/tmp/path/execute.php:6-8}() /tmp/path/execute.php:0
    0.0036     241624   4. spl_autoload() /tmp/path/execute.php:7

Thank you very much, you save my days

I face the same issue but in my case the opcache.enable_cli flag doesn't actually affect the problem. For now, I don't really know what causes the problem but in my machine the problem does not exist but on the server it exists. In both cases the opcache.enable_cli is disabled.

My machine (there's no problem)

PHP 7.0.2-4+deb.sury.org~trusty+1 (cli) ( NTS )
Copyright (c) 1997-2015 The PHP Group
Zend Engine v3.0.0, Copyright (c) 1998-2015 Zend Technologies
    with Zend OPcache v7.0.6-dev, Copyright (c) 1999-2015, by Zend Technologies

The server (the error gets thrown)

PHP 7.0.0 (cli) (built: Dec  9 2015 09:25:52) ( NTS )
Copyright (c) 1997-2015 The PHP Group
Zend Engine v3.0.0, Copyright (c) 1998-2015 Zend Technologies
    with Zend OPcache v7.0.6-dev, Copyright (c) 1999-2015, by Zend Technologies

excellent work.

without opcache:

https://gist.github.com/wandersonwhcr/e16e9dcfb2c54dafa2f84c145b0de983

same problem

5.6.30 - actual

5.5.30，the same issue occurs when opcache is disabled and disappears when opcache is enabled.