When I run this on my Mac, I get this:

$ java -jar src/server/jruby/jruby-complete-1.7.16.jar -e "puts Gem"
Gem

But with the exact same JAR file on Windows (8.1, but it hardly matters):

Y:\some-path>java -jar src\server\jruby\jruby-complete-1.7.16.jar -e "puts Gem"
NameError: uninitialized constant Gem
  const_missing at org/jruby/RubyModule.java:2723
         (root) at -e:1

Why is this? The Java version is JRE 8u20 on Mac. On Windows, I've tested with both JRE 8u20 and 7u45.

I did some more testing before committing the issue. It turned out that it works if I copy the jruby-complete .jar to my local C: drive, instead of running it from my Mac home folder (which is essentially a network folder - I run my Windows in a Parallels VM).

Nonetheless, this has worked flawlessly with older JRuby (1.7.6), so it's very likely this is the same issue as some of the other open jruby-complete issues that are open at the moment.