Remote file URL for XML import of grades broken?

It looks like the import of grades from a remote URL is not working. I asked in the forum but got no confirmation if the error is at my part or Moodle.

It is not working from any location (localhost or remote). I tried a freshly exported file with the same outcome. I even used different Moodle versions (2.2.2+ and 2.2.1+) on different servers with the same effects. What is strange about it is, that I can import the file when I choose to upload it.

Also the debug info shows a 404 error, but I can access the file through my browser:

Output buffer: <div class="notifytiny">cURL request for "http://localhost/moodle/grade/import/xml/import.php?id=2&amp;url=http%3A%2F%2Flocalhost%2Fmoodle%2Fimport_or.xml" failed, HTTP response code: HTTP/1.1 404 Not Found <ul style="text-align: left"><li>line 1153 of \lib\filelib.php: call to debugging()</li><li>line 49 of \grade\import\xml\import.php: call to download_file_content()</li></ul></div>