Wiki server, can't delete people

We are using OS X Server 10.7 on an Xserve. I'm wanting to upgrade to Mavericks server, but I am told the following issue still exists. I called this a bug because it is basic functionality that I cannot perform. In our school, we have many people who used the collaboration server to create wikis, blogs, upload files, etc.

However, the problem is, when the students leave the school, or staff members leave the organization, there is no way to remove them from the People section of the collaboration server. This is an issue since we have a list of people that have nothing to do with our organization, yet they are still there! They log in using their Active Directory credentials - we are not using Profile Manager.

I've called Apple support, and they were unable to tell me how to remove people from the list. Has anyone else come across a solution?