I've already been testing this solution to see if it solves the PHP mail problem. It seemed to work OK but you are giving me more confidence.
If you want to send attachments don't add $attach as a new variable to the function. It's an array anyway and I can't get the built in WP function to behave. The MIME boundaries are delicate creatures and when you send the attachment it doesn't display properly in the email client.
So just use:
wp_mail( $qcf_email, $subject, $message, $headers);
and let the plugin look after the attachments for you