This is possible the user has a hub login license. These licenses are part of the new license model. In case you still have Corporate/ Ultimate licenses, please contact your sales representative. Under Set Up > Manage Users & Access Rights > Access Rights you can assign rights to these users or the user group. When a user has the H(ub) Right on a folder, he can see all published diagrams in the published revision of the folder. When the user has as well the R(ead) right, he can see as well the unpublished diagrams and newer revisions of the diagrams of this folder. By default, the links for Hub Licence Users to the Explorer and the Preview-Hub are not displayed. You need to activate them under Setup > Manage Collaboration Hub Configuration. Please activate the check box at "Enable view switch for Hub license users".