Description:
------------
Kinda hard to explain, better look at the code below.
The leak is only reproducible when return value is used, remove $var and it's gone.

Reproduce code:
---------------
<?php
function err($errno, $errstr, $errfile, $errline)
{
    throw new Exception($errstr);
}

set_error_handler("err");

class test {
    function foo() {
        $var = $this->blah->prop = "string";
        var_dump($this->blah);
    }
}

$t = new test;
try {
    $t->foo();
} catch (Exception $e) {
    var_dump($e->getMessage());
}
?>

Actual result:
--------------
==11422== 7 bytes in 1 blocks are indirectly lost in loss record 1 of 2
==11422==    at 0x401C6CE: malloc (vg_replace_malloc.c:149)
==11422==    by 0x82BEA9F: _emalloc (zend_alloc.c:2231)
==11422==    by 0x82BED45: _estrndup (zend_alloc.c:2353)
==11422==    by 0x82D75CF: _zval_copy_ctor_func (zend_variables.c:120)
==11422==    by 0x833BDD4: _zval_copy_ctor (zend_variables.h:45)
==11422==    by 0x833D047: zend_assign_to_object (zend_execute.c:593)
==11422==    by 0x830DA7A: ZEND_ASSIGN_OBJ_SPEC_VAR_CONST_HANDLER (zend_vm_execute.h:9226)
==11422==    by 0x82F8680: execute (zend_vm_execute.h:92)
==11422==    by 0x82F8BA2: zend_do_fcall_common_helper_SPEC (zend_vm_execute.h:234)
==11422==    by 0x82F8FB9: ZEND_DO_FCALL_BY_NAME_SPEC_HANDLER (zend_vm_execute.h:322)
==11422==    by 0x82F8680: execute (zend_vm_execute.h:92)
==11422==    by 0x82D92F7: zend_execute_scripts (zend.c:1134)
==11422==    by 0x828FE7C: php_execute_script (main.c:1790)
==11422==    by 0x833FA35: main (php_cli.c:1127)
==11422==
==11422==
==11422== 23 (16 direct, 7 indirect) bytes in 1 blocks are definitely lost in loss record 2 of 2
==11422==    at 0x401C6CE: malloc (vg_replace_malloc.c:149)
==11422==    by 0x82BEA9F: _emalloc (zend_alloc.c:2231)
==11422==    by 0x833CFFF: zend_assign_to_object (zend_execute.c:589)
==11422==    by 0x830DA7A: ZEND_ASSIGN_OBJ_SPEC_VAR_CONST_HANDLER (zend_vm_execute.h:9226)
==11422==    by 0x82F8680: execute (zend_vm_execute.h:92)
==11422==    by 0x82F8BA2: zend_do_fcall_common_helper_SPEC (zend_vm_execute.h:234)
==11422==    by 0x82F8FB9: ZEND_DO_FCALL_BY_NAME_SPEC_HANDLER (zend_vm_execute.h:322)
==11422==    by 0x82F8680: execute (zend_vm_execute.h:92)
==11422==    by 0x82D92F7: zend_execute_scripts (zend.c:1134)
==11422==    by 0x828FE7C: php_execute_script (main.c:1790)
==11422==    by 0x833FA35: main (php_cli.c:1127)