The ones that are clearing out are the ones that you have bound directly to the posted form from the previous page like:
<input name="usef" type="hidden" id="usef" value="<?php echo((isset($_POST["usef"]))?$_POST["usef"]:"") ?>" />
Instead you should be posting the previous page to itself and storing those as session variables. Then redirecting to this page and populating the hidden form elements from the session like you do the other fields.