Membership Plugin Not Protecting Media Downloads

I'm having an insane amount of trouble trying to get Memebership to protect media downloads on my site. Here's want I want to happen:

1) Free ESL audio is available for non-paying members.

2) Links to extra material like downloadable versions of the audio, vocab lists and transcripts are posted in the sidebar. I'd like non-paying members to be redirected to a sign-up page/subscription page where they can sign-up or they can upgrade their subscription.

What is actually happening:

1) Media is added through the media library uploader.

2) I choose/create a protected content group. Free Account and Visitor levels have a negative rule added to prevent downloading media inside that media group.

3) Audio and PDFs are added to the post where the lesson is.

4) Everyone is able to download the extra (premium) material without paying a dollar for all my hard work.

This site is aimed at provided ESL material for Chinese students (it's a lot of hard work translating), but right now, I'm spending twice as much time chasing my tail trying to get this plugin to do what it's supposed to rather than putting out content on the site.

A sample page is available to view at http://www.redlanternconsulting.com/lesson/the-pub/

I tried for three hours today to get it to work, and I give up. Over to you guys...