The community invitation makes the new user to enter on the environment, but do not auto-join on the community.
The community invitation does not works for already registered user, proving that is a environment invitation and not a community invitation.
The problem was found at http://netica.org.br/myprofile/educadores/profile_members
Clicking on the button "Convide seus amigos para entrar em Educadores"
You are redirected to http://netica.org.br/profile/educadores/invite/friends ,
where the title is "Convide seus amigos para entrar em Educadores"
-- AurelioAHeckert -- 23 Apr 2010
I've tested in a local and up to date noosfero set up and both the community invitation and friend invitation make the new user auto-join the community/auto-friend the requester. Also, when I tested, invitation does work if you put an email for an already registered user (the invitation appears on the invited user's tasks).
-- LarissaReis - 05 Jun 2012