This question is an exact duplicate of:
The URL recognizer stops at the
' character, yet this is a valid character in URLs.
On a related note, wrapping the URL in
<a href="..."> doesn't help either; somehow the sanitizing process filters out the URL it thinks is faulty:
<a href="http://en.wikipedia.org/wiki/Rice's_theorem">this is (not) a link</a>
<p>this is (not) a link</p>
(Currently: this is (not) a link.)