Description:
------------
str_replace() not replacing entire search string with its replacement.

Reproduce code:
---------------
<?php
$s = array (
  0 => '%host', 1 => '%login',
  2 => '%user', 3 => '%time',
  4 => '%method', 5 => '%url',
  6 => '%protocol', 7 => '%status',
  8 => '%bytesSent', 9 => '%referrer',
  10 => '%userAgent',
);
$r = array (
  0 => '([^ ])+', 1 => '([^ ])+', 
  2 => '([^ ])+', 3 => '([^\\]])+',
  4 => '([^ ])+', 5 => '([^ ])+',
  6 => '([^"])+', 7 => '([^ ])+',
  8 => '([^ ])+', 9 => '([^"])+',
  10 => '([^"])+',
);
$subject = '%host %login %user [%time] "%method %url %protocol" %status %bytesSent "%referrer" "%userAgent"';

echo str_replace($s, $r, $subject), "\n";

Expected result:
----------------
([^ ])+ ([^ ])+ ([^ ])+ [([^\]])+] "([^ ])+ ([^ ])+ ([^"])+" ([^ ])+ ([^ ])+ "([^"])+" "([^ ])+"

Actual result:
--------------
([^ ])+ ([^ ])+ ([^ ])+ [([^\]])+] "([^ ])+ ([^ ])+ ([^"])+" ([^ ])+ ([^ ])+ "([^"])+" "([^ ])+Agent"