I found a strange behavior when trying to upload a document from the front end.
I'm logging in with a user who has full rights in categories. When I click on UPLOAD the user looks to logging out becasue in the Joomla's login form shows empty username and pasword again not the user who has logged in before.
However the uploading form appears and I can fill the input boxes but I can't upload anything because I get a "Error Save not Permited" message.