I would have to say you also do not have category permissions set correctly then if usergroups are set.
If you logins are not in sync it is because you have not set them up correctly. As I say the same to people who use VB3 all the time.
I have IB2 and Reviewpost install here and the logins are always integrated
http://www.omegatron.net/reviews/ http://www.omegatron.net/ib/
You can login with photopost and alphabeta