title: Strange behaviour of Convert.FromBase64String
body: <p>Why does the following code</p>
  
  <pre><code>var s =  "2I==";
  var b = Convert.FromBase64String(s);
  var new_s = Convert.ToBase64String(b);
  </code></pre>
  
  <p>end up with new_s being <code>2A==</code>?</p>
  
  <p><code>s</code> was originally a longer string (96 chars) but I couldn't include it because it is a secret key.</p>