User purchases Membership through Marketpress cart but is not added to user or members

We've got 4 Membership level products set up in Marketpress. I can go through an entire checkout process and it completes the order, but it's never added to the All Members list, nor is an email generated with user name and password. I go through and mark the order as Paid but still never gets added.
I checked the Products in Marketpress and they are associated with the 2 Access Levels we've got set up.
We are not using the Subscription Pages and checkout through Membership, we are doing the checkout through Marketpress. I'm wondering if that's the problem and we'll have to have 2 separate shopping carts instead (which would be confusing I think)?

Thanks for any help! If you want to see the configuration, I'll be happy to show you.