Code executing twice

I have a page that executes a PHP script. Page content is very simple:
<?php
include “myscript.php”;
?>

myscript.php has code that loads a form (code piece 1), and then some more code that executes when the form is submitted (code piece 2). The problem I’m running into, is that Code piece 2 is executing twice. I checked and double checked my code, and there’s no chance that I have a loop that executes twice. Code piece 2 checks to see if a piece of data is in the database, and if it’s not, insert it. As a result of the double execution, the answer is yes, it’s in the database every single time.

Theme is thesis_18. Any ideas?