change:
<form action="listing_Insert.php" method="post" name="WADAInsertForm" id="WADAInsertForm">
to:
<form action="listing_Insert.php" method="post" name="WADAInsertForm" id="WADAInsertForm" enctype="multipart/form-data">
That's the ticket! After that change everything works fine now...
I wonder how the insert was working when the POST data type wasn't set to forms data?
So I guess the lesson learned here is that when adding an upload to an existing DA form the data type needs to be changed by hand.