I have two problems.
1. I've the same problem other users have had, that being that the invite code field is being replicated for every field under Profile Details on the Registration page. I encountered this first on my primary site. After much troubleshooting without resolution, I decided to create a fresh WordPress/BuddyPress installation in another domain I have. It has the same problem here. I'm using the latest versions of WP, BP and Membership plugin v 3.4.5 RC 3. This is the version that was used to resolve this issue for another user on this site.
2. Even with the option selected to Require Invite Codes in Membership/Settings/Extras. It still allows registrations to be made and accepted without Invite Codes being entered.