submitting a GET form with query string params and hidden params disappear

Question

Consider this form:

Answer 1

This is in response to the above post by Efx:

If the URL already contains the var you want to change, then it is added yet again as a hidden field.

Here is a modification of that code as to prevent duplicating vars in the URL:

foreach ($_GET as $key => $value) {
    if ($key != "my_key") {
        echo("");
    }
}