The "sources" jar (at least since Clojure 1.4 and including 1.5 RC) has a bad version.properties file in it. The resource clojure/version.properties is literally:
The regular Clojure jar has the correct version string in that resource.
I came across a problem when I was experimenting with the sources jar (as used by IDEs). I naively added the sources jar to my classpath, and Clojure died on start up. The bad clojure/versions.properties file was found first, which led to a parse error as the clojure version was being set.