Description:
------------
If an instance of ArrayObject $ao has flag ArrayObject::ARRAY_AS_PROPS set, $ao->p will access element p of the underlying storage array - but only if no real property p exists on $ao. If a real property p does exist, it will access that property as if the flag were not set.

This works correctly with read, write and unset, but not with isset:
when a real property p exists, isset($ao->p) always returns false .

Reproduce code:
---------------
<?php
class C extends ArrayObject {
	public $p = 'object property';
}	

$ao = new C(array('p'=>'array element'));
$ao->setFlags(ArrayObject::ARRAY_AS_PROPS);

echo "\n--> Access the real property:\n";
var_dump(isset($ao->p));  // bug
var_dump($ao->p);

echo "\n--> Remove the real property and access the array element:\n";
unset($ao->p);
var_dump(isset($ao->p));
var_dump($ao->p);

echo "\n--> Remove the array element and try access again:\n";
unset($ao->p);
var_dump(isset($ao->p));
var_dump($ao->p);
?>

Expected result:
----------------
--> Access the real property:
bool(true)
string(15) "object property"

--> Remove the real property and access the array element:
bool(true)
string(13) "array element"

--> Remove the array element and try access again:
bool(false)

Notice: Undefined index:  p in %s on line 21
NULL

Actual result:
--------------
--> Access the real property:
bool(false)
string(15) "object property"

--> Remove the real property and access the array element:
bool(true)
string(13) "array element"

--> Remove the array element and try access again:
bool(false)

Notice: Undefined index:  p in %s on line 21
NULL