Description:
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When using array_shift() on an array and then adding new elements in it, the index is incremented in a wrong way.

this behavior differs from previous PHP versions (working in PHP 5.6-alpha1, broken in beta1 and beta2)

Test script:
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<?php

$a = array();
$a[] = 1;
var_dump(array_keys($a));
array_shift($a);
$a[] = 1;
var_dump(array_keys($a));

Expected result:
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array(1) { [0]=> int(0) } 
array(1) { [0]=> int(0) }

Actual result:
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array(1) { [0]=> int(0) } 
array(1) { [0]=> int(1) }