We are using an AD group which is a Universal Security group as a target audience on a Web Part. Our environment is SharePoint 2010, SP1. When we add the target audience it only shows 3 of the 5 members. We do not actually see who the members are just the number of members. 2 of the members cannot see the web part and the other 3 can. I've checked the individual users and they all have access to the site as the group has full control.