From http://jira.codehaus.org/browse/JRUBY-6656. See that issue for attached reproduction files.

I subclass a Java class that has a varargs constructor in JRuby, the JRuby class attempts to call super(a,b) to invoke the superclasses constructor and this fails with:
ArgumentError: wrong number of arguments for constructor
initialize at varargsctor.rb:6
(root) at varargsctor.rb:11
Invoking super(nil) works, but super() and super(a,b) fail.
Sample Java class and JRuby subclass attached.