actually, this is not a only reflection specific issue.

<?php
namespace Foo\Bar\A\B;

interface BInterface {}

class Foo implements BInterface {
}

namespace Foo\Bar;
use A\B\BInterface;

class Bar implements BarInterface {
    public function __construct()
    {
        echo "Hello!";
    }

    public function getSomething(BInterface $b){}
}

interface BarInterface {
        public function getSomething(BInterface $b);
}

namespace TestNamespace;

use Foo\Bar\A\B;
$obj = new \Foo\Bar\Bar();
$arg = new \Foo\Bar\A\B\Foo;
$obj->getSomething($arg);


PHP Catchable fatal error:  Argument 1 passed to Foo\Bar\Bar::getSomething() 
must be an instance of A\B\BInterface, instance of Foo\Bar\A\B\Foo given, called 
in /tmp/1.php on line 30 and defined in /tmp/1.php on line 18


dmitry, could you please look at this one?

I have tried to make a fix, but for such situation

use \Foo;  CG(current_import) only hold the Foo name but doesn't hold the global 
name flag..

so, I can not simply resolve the full name of a class name which is imported and 
in a namespace.

PHP doesn't support *relative* namespace import. A name from "use" statement is always used as a full namespace name.