FTPWebRequest suddenly sends a USER command?

[Håvard Olerud Eriksen]

I've got a small utility here that downloads the contents of some
directory. Now, the weird thing is that sometimes I get an exception
when I start the download of a new file.
The exception I get is: The remote server returned an error: (500)
Syntax error, command unrecognized. I then used the Network Monitor to
track the traffic and it turns out that intermittently my app sends a
USER request to the server, which in turn returns the 500 message as
it's expecting a GET request.
There is no pattern as to which files it does this for, and it varies
from run to run.

The skeleton is basically ripped from the MS tutorial with some small
changes done by me.
It first connects and requests a listing off all the files in the
directory. I then pass the filename + the FtpWebRequest onto the
download function. At the start of the function I use the request and
create a new request and change the Method to Download file. If all
goes well it downloads the file.
connRequest = (FtpWebRequest)WebRequest.Create(downloadUrl);

I've got a nagging suspision that this ^ request creates the USER
request, but then, how come it doesn't do this for every single file?

connRequest.Method = WebRequestMethods.Ftp.DownloadFile;

Any help is much appreciated.

Håvard