The author's editing of metadata should be locked when submissions are archived, declined, or if there are open reviews against the submission. This is handled by classes/submission/author/AuthorAction.inc.php, in the function mayEditPaper. If you are seeing the edit metadata link on a submission when it shouldn't be there (i.e. on the conf/schedConf/author/submission/id page), it may be because you are logged in as a director or track director (as you can see in the function, users with that role will always be able to edit metadata). Have you tried logging in as the author of a paper, where the author only has the author role, and been able to edit a paper's metadata?
Public Knowledge Project Team