404 errors repeatedly sent using http_response_code?

I am trying to send http headers. I have used both

header(“HTTP/1.0 404 Not Found”);

and

http_response_code(404);

Both work fine. But both seem to send the error code multiple times (4 times, to be exact) when I monitor the http responses via HttpFox.

But if I use this code, found on the http_response_code page (http://us1.php.net/http_response_code)

// Get the current default response code
var_dump(http_response_code()); // int(200)

// Set our response code
http_response_code(404);

// Get our new response code
var_dump(http_response_code()); // int(404)

I only monitor one response from the server.

Can someone explain to me if this is normal behavior, and if not, what I should be doing?

Tests were done in empty php files, just with the code provided above.