If there is to be any difference between IE and the other browsers, it must be in the way they return the parameters to your server.

The server doesn't care which type of browser is "listening", so you should try to find out what gets returned to the server by your form.

Best way to do that is to set the "action" field in your form to another script that simply does a Data::Dumper of your CGI-object and see if your get a different return from IE and the other browsers.