Just try to run jruby --debug -S rdebug --help. With 1.1.4 works, with 1.1.5 the debugger does not work.
It is likely due to require semantics. In $YOUR_GEM_REPO/gems/ruby-debug-base-0.10.2-java/lib/ruby-debug-base.rb there is:
tracelines.rb and linecache are in the same directory as ruby-debug-base.rb. Workaround is to change the lines to:
The reasons I made path relatives is to prevent collision with tracelines and linecache files from other gem.