Description:
------------
When an error handler is called because of a undefined property and the error handler references a different object property that doesn't exist, even in an isset(), the original property gets replaced by the new property in the operation that was being performed.

I ran a git bisect to find the commit that introduced the error and found the following commit:
commit 0c6d903ce7615a7197cb997d67d98058c3ec5d6a
Author: Stanislav Malyshev <stas@php.net>
Date:   Mon Feb 18 20:56:02 2013 -0800

    fix bug #49348 - issue notice on get_property_ptr_ptr when used for read


Test script:
---------------
<?php
function err_handler()
{
      $s = new StdClass();
      isset($s->bad);
}

set_error_handler('err_handler');

$f->good += 5 ; 

var_export($f);

if(isset($f->bad))
    exit(1);
else
    exit(0);


Expected result:
----------------
stdClass::__set_state(array(
   'bad' => 5,
))

With an Exit value of 1

Actual result:
--------------
stdClass::__set_state(array(
   'good' => 5,
))

With an Exit value of 0