Older documents have a lot of links similar to http://dev.clojure.org/jira/browse/CLJ-2438. Currently, following them leads to https://clojure.atlassian.net/browse/undefined, so all those old links have been pretty much 404'ed.
The new URL should be https://clojure.atlassian.net/browse/CLJ-2438, which seems like a very simple rewrite rule. Perhaps it could be implemented?