This is probably not really bug, just a missing feature.

Basically the fopen()URL handler doesn't allow the specification of an alternativ port within the url such as

http://hostname:port/path/file.html

I guess it will probably also not handle http://user:pass@host/, so maybe you could add that as well sometime.

the following script:
  <?php
    readfile('http://localhost:8080/');
  ?>

results in the following output:

X-Powered-By: PHP/4.0.6
Content-type: text/html

<br>
<b>Warning</b>:  readfile("http://localhost:8080/") - Success in <b>-</b> on line <b>2</b><br>