Reminder to self: AS_END is returned when updateArticle() fails. We don't check for insertNewArticle()'s return value, though, while we probably should.

Fixed in r40383, but not probably not the way you expected ;)

AS_END is only returned if something weird happens, like an UPDATE on page_latest failing because it was UPDATEd after the edit conflict check. Similar conditions are possible for other write operations (such as move and rollback), and they, too, return 'unknownerror'. As documented on [[mw:API:Errors and warnings]] (added it just now, but it was there when the errors were still listed on separate pages), 'unknownerror' really means that something very weird happened and that you should retry the request.