i think i have found a bug, but i am unsure. Moreover i dont have an SF-Account for Bugtracker.
I have notice if i give the group "everybody" the Manage-Right for the Module "Mail", and decrease the right later from "Manage" to "Use" the User dont have access to any Module anymore (Message "No Module configured...").
If i set the rights for Module "Files" from "Use" to "no rights" (first option) i expect the User in this group dont see the "Files"-Tab anymore, but its still there and selectable.
yes... like i decribed, first i wanted decrease all rights and got this problem. After i give back the formaly rights, evth was ok... then in have searched what is responsible for this. result: if i just change the rights from mail and this behavior will be happen.