Problem/Motivation
Default taxonomy term view does not have "Publishing status" filter but accepts an exception value 'all' for "Has taxonomy term". With exception value in URL, the page display returns 404 (this may be a separate bug) but the feed display correctly ignores the argument and displays all results including unpublished nodes.
Steps to reproduce: Install, create an unpublished article and visit /taxonomy/term/all/feed.
Proposed resolution
Add the status filter or remove exception value or both.