Missing $_POST Data

After a sermon submission with attachment, why does the $_POST[‘sermon_audio_id’] variable show up blank? Yet $_POST[‘sermon_audio’] has the correct URI to the file.

It would save me an iffy SQL query, if I actually had the ID of the post (type “attachment”) that is a child of the main sermon post. I’m curious as to why this field is left blank, but tantalizingly sent along in the $_POST variable:

http://wordpress.org/extend/plugins/sermon-manager-for-wordpress/