IE Displaying force_download Output to Screen

[eluser]ladyj001[/eluser]
I am experimenting with the force_download function of the Download Helper. I am currently trying to implement the example given in the user guide.

$this->load->helper('download');
$data = 'Here is some text!';
$name = 'mytext.txt';
force_download($name, $data);

In FF, the Open/Save dialog box appears as expected. But, in IE7, the output is displayed directly on the screen. There is no Open/Save prompt. What am I doing wrong?