Description:
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When assigning a reference to a previously undefined property of an ArrayObject, 
E_NOTICE is thrown on the assignment itself, and every time that property is 
accessed after that. Despite the "undefined index" complaints, the code works as 
expected — $b->test[] = "foo" successfully assigns "foo" to $a[0].

This issue does not occur with assignment by value — no notices are displayed 
(though the code no longer works as intended, as $a[0] remains undefined). It also 
does not occur if $b->test is initialized prior to the assignment by reference 
(e.g. adding a "$b->test = true" row before the assignment) — in this case the 
assignment by reference also works as intended, and does not emit E_NOTICE.

Test script:
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error_reporting(E_ALL & E_STRICT);
ini_set('display_errors', 1);

$a = array();
$b = new ArrayObject(array(), ArrayObject::ARRAY_AS_PROPS);
$b->test = &$a;
$b->test[] = "foo";
print($a[0]);

Expected result:
----------------
Script should run without notices.

Actual result:
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Script throws "Undefined index: test" notices every time $b->test is referenced, 
even though everything works correctly otherwise.