title: str_replace with array
body: <p>I'm having some troubles with the PHP function <code>str_replace</code> when using arrays.</p>
  
  <p>I have this message:</p>
  
  <pre><code>$message = strtolower("L rzzo rwldd ty esp mtdsza'd szdepw ty esp opgtw'd dple");
  </code></pre>
  
  <p>And I am trying to use <code>str_replace</code> like this:</p>
  
  <pre><code>$new_message = str_replace(
      array('l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','a','b','c','d','e','f','g','h','i','j','k'),
      array('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'),
      $message);
  </code></pre>
  
  <p>The result should be <code>A good glass in the bishop's hostel in the devil's seat</code>, but instead, I get <code>p voos vlpss xn twt qxswop's wosttl xn twt stvxl's stpt</code>.</p>
  
  <p>However, when I only try replacing 2 letters it replaces them well:</p>
  
  <pre><code>$new_message = str_replace(array('l','p'), array('a','e'), $message);
  </code></pre>
  
  <p>the letters <code>l</code> and <code>p</code> will be replaced by <code>a</code> and <code>e</code>.</p>
  
  <p>Why is it not working with the full alphabet array if they are both exactly the same size?</p>