The Druapl ‘request_uri’ function in includes/bootstrap.inc always adds a slash to the beginning of the server variable REQUEST_URI, which will break any absolute URLs.

The following modification (the strpos check) resolves this issue:

/**
* Since $_SERVER['REQUEST_URI'] is only available on Apache, we
* generate an equivalent using other environment variables.
*/
function request_uri() {
  if (isset($_SERVER['REQUEST_URI'])) {
    $uri = $_SERVER['REQUEST_URI'];
  }
  else {
    if (isset($_SERVER['argv'])) {
      $uri = $_SERVER['SCRIPT_NAME'] .'?'. $_SERVER['argv'][0];
    }
    else {
      $uri = $_SERVER['SCRIPT_NAME'] .'?'. $_SERVER['QUERY_STRING'];
    }
  }
  if (strpos($uri, '/') == 0)
  {
    // Prevent multiple slashes to avoid cross site requests via the FAPI.
    $uri = '/'. ltrim($uri, '/');
  }
  return $uri;
}