Name field case sensitive when logging in to a WIKI?

Why is the name field case sensitive, when a user tries to acces a Wiki hosted on Mac OS Server 10.6? It really took me some time to figure out why my users were rejected when trying to login. But it seems to be the case that the user name field is case sensitive (which is not the case for all other logins in the Mac invironment. Does anyone know how to eventually turn it off?