seems not to be really a bug, as the manual explains the following:
http://de.php.net/manual/en/language.oop5.visibility.php
"Class members declared public can be accessed everywhere. Members declared protected can be accessed only within the class itself and by inherited and parent classes. Members declared as private may only be accessed by the class that defines the member."

BUT

there is something wrong.. It seems somehow __get will be invoked on the "parents scope" if not redefined...

Test script:
------------
<?php
class Foo {
	private $var = 'sheep';
	function __construct() {
	}
	public function __call($f,$a) {
		return empty($this->{$f});
	}
	public function __get($v) {
		return $this->{$v};
	}
}
class Bar extends Foo {
}
class Baz extends Foo {
	private $var;
	function __construct() {
		$this->var = 'dog';
	}
}
class Faz extends Foo {
	private $var;
	function __construct() {
		$this->var = 'cat';
	}
	function __call($f,$a) {
		return empty($this->{$f});
	}
	function __get($v) {
		return $this->{$v};
	}
}
$test = new Foo();
echo('called $Foo->var(): '.(int)$test->var().PHP_EOL);
echo('called $Foo->var: '.$test->var.PHP_EOL);
echo('existing property: '.property_exists($test,'var').PHP_EOL);
$test = new Bar();
echo('called $Bar->var(): '.(int)$test->var().PHP_EOL);
echo('called $Bar->var: '.$test->var.PHP_EOL);
echo('existing property: '.property_exists($test,'var').PHP_EOL);
$test = new Baz();
echo('called $Baz->var(): '.(int)$test->var().PHP_EOL);
echo('called $Baz->var: '.$test->var.PHP_EOL);
echo('existing property: '.property_exists($test,'var').PHP_EOL);
$test = new Faz();
echo('called $Faz->var(): '.(int)$test->var().PHP_EOL);
echo('called $Faz->var: '.$test->var.PHP_EOL);
echo('existing property: '.property_exists($test,'var').PHP_EOL);
?>

Expected result:
----------------
called $Foo->var(): 0
called $Foo->var: sheep
existing property: 1
called $Bar->var(): 1 <-----
called $Bar->var:  <-----
existing property: 
called $Baz->var(): 0
called $Baz->var: dog <-----
existing property: 1
called $Faz->var(): 0
called $Faz->var: cat
existing property: 1

Actual result:
--------------
called $Foo->var(): 1
called $Foo->var: sheep
existing property: 1
called $Bar->var(): 0
called $Bar->var: sheep
existing property: 
called $Baz->var(): 0
called $Baz->var: sheep
existing property: 1
called $Faz->var(): 0
called $Faz->var: cat
existing property: 1

addition to my previous post..

toggling the default value of $var in Foo to null and setting it in the constructor:
<?php
class Foo {
	#private $var = 'sheep';
	private $var;
	function __construct() {
		$this->var = 'sheep';
	}
...
?>

will effect to the following result:
------------------------------------
called $Foo->var(): 0
called $Foo->var: sheep
existing property: 1
called $Bar->var(): 0
called $Bar->var: sheep
existing property: 
called $Baz->var(): 1 <-----
called $Baz->var:  <-----
existing property: 1
called $Faz->var(): 0
called $Faz->var: cat
existing property: 1

Hi rayro!
Thank you for your answer!

I think magic methods must be independent of the place of the declaration.

This is a problem here:
$this and property_exists($this, $prop) is in right scope (test class)
get_class_vars(get_called_class()) and isset($this->$prop) is in parent scope (base class)

This is expected behavior. __get is a method of base, hence its *calling* scope will be "base" and it will only be able to access private properties of base.

The *called* scope is a different matter altogether (see php.net/lsb); in case of non static calls it will be set to the runtime class of the object, but it's not used to determine access to properties (or methods).