on setting the session:
<?php
// Set session for sticky searches
if (!session_id()) session_start();
if((((isset($_POST["searchbox"]))?$_POST["searchbox"]:"") != "")) {
$_SESSION["mrsSearchActive"] = "".((isset($_POST["searchbox"]))?$_POST["searchbox"]:"") ."";
}
else if((((isset($_POST["searchbox"]))?$_POST["searchbox"]:"") == "")) {
$_SESSION["mrsSearchActive"] = "0";
}
?>
your else statement is resetting the session if no form is submitted.
change that so it only sets the session if the form is submitted, and does nothing if it is not:
<?php
// Set session for sticky searches
if (!session_id()) session_start();
if((((isset($_POST["searchbox"]))?$_POST["searchbox"]:"") != "")) {
$_SESSION["mrsSearchActive"] = "".((isset($_POST["searchbox"]))?$_POST["searchbox"]:"") ."";
}
?>