I discussed this with kate back then and I said that the tabs should be shown with an error message instead of hiding to let users know what is wrong. In our old popup we simply didn't show the upload form when permissions where missing. This resulted in http://www.dokuwiki.org/faq:upload
because user didn't know what is wrong.
The error text in the edit tab is a bit strange but correct. Because the permission to edit metadata is AUTH_UPLOAD.