Quick question about order of PHP code at start of page

I have DB Update page that is just being used to add images and a PDF to a record just created on a previous page. The set up is a bit convoluted, but this page is the third of a sequence.

In addition to the DB code to update the record and upload the files, there is some code which inserts some keywords into a related table, using the code below:

<?php

/********************
*
*insert Lodge Activities into the LodgeActivities table
*
********************/

//sql insert string

$sql = "INSERT INTO ItineraryActivities (ItineraryID, ActivityID) VALUES ";

$ck = $_GET['ckbox'];

//loops though the profiles adding the insert string each profile row

foreach ($ck As $GetIndex => $GetValue){
if ($GetValue=='on'){
$sql .= "('{$_GET['ItineraryID']}', '$GetIndex'), ";
}
}

//trims the end , 

$sql = rtrim($sql," ,") ;

//inserts data

mysql_select_db($database_connSafari, $connSafari); mysql_query($sql); echo mysql_error();
?>

This code appears after the DB Update / Upload code, ie immediately before the <DOCTYPE> declaration.

So when the page first loads, it ignores the DB Update / Upload code, and executes the code above, correctly inserting the keywords.

However, when the form is submitted, and executes the DB Update / Upload code, its also executing the code above a again, and creating duplicate records.

Should that happen, or should that part not be executed on form submission, because it would only get as far as the redirect in the DB Update / Upload code before it?

Hope that makes sense - I've attached the page for reference.